Fixes to make all unit tests pass

- Also fix some formatting warnings

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -252,9 +252,10 @@ namespace SixLabors.ImageSharp.Formats.Png
 
                                 using (var deframeStream = new ZlibInflateStream(this.currentStream, this.ReadNextDataChunk))
                                 {
-									deframeStream.AllocateNewBytes(chunk.Length);
+                                    deframeStream.AllocateNewBytes(chunk.Length);
                                     this.ReadScanlines(deframeStream.CompressedStream, image.Frames.RootFrame);
                                 }
+
                                 break;
                             case PngChunkType.Palette:
                                 byte[] pal = new byte[chunk.Length];
@@ -1376,16 +1377,23 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// <returns>Count of bytes in the next data chunk, or 0 if there are no more data chunks left.</returns>
         private int ReadNextDataChunk()
         {
-            this.currentStream.Read(this.crcBuffer, 0, 4);
+            if (this.nextChunk != null)
+            {
+                return 0;
+            }
 
-            this.TryReadChunk(out PngChunk chunk);
+            this.currentStream.Read(this.crcBuffer, 0, 4);
 
-            if (chunk.Type == PngChunkType.Data)
+            if (this.TryReadChunk(out PngChunk chunk))
             {
-                return chunk.Length;
+                if (chunk.Type == PngChunkType.Data)
+                {
+                    return chunk.Length;
+                }
+
+                this.nextChunk = chunk;
             }
 
-            this.nextChunk = chunk;
             return 0;
         }
 
@@ -1401,6 +1409,9 @@ namespace SixLabors.ImageSharp.Formats.Png
             if (this.nextChunk != null)
             {
                 chunk = this.nextChunk.Value;
+
+                this.nextChunk = null;
+
                 return true;
             }
 

src/ImageSharp/Formats/Png/Zlib/ZlibInflateStream.cs

@@ -42,11 +42,6 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
         /// </remarks>
         private bool isDisposed;
 
-        /// <summary>
-        /// Whether the crc value has been read.
-        /// </summary>
-        private bool crcRead;
-
         /// <summary>
         /// The current data remaining to be read
         /// </summary>
@@ -119,17 +114,36 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
         {
             if (this.currentDataRemaining == 0)
             {
-				this.currentDataRemaining = this.getData();
+                // last buffer was read in its entirety, let's make sure we don't actually have more
+                this.currentDataRemaining = this.getData();
 
-				if (this.currentDataRemaining == 0)
-				{
-					return 0;
-				}
+                if (this.currentDataRemaining == 0)
+                {
+                    return 0;
+                }
             }
 
             int bytesToRead = Math.Min(count, this.currentDataRemaining);
             this.currentDataRemaining -= bytesToRead;
-            return this.innerStream.Read(buffer, offset, bytesToRead);
+            int bytesRead = this.innerStream.Read(buffer, offset, bytesToRead);
+
+            // keep reading data until we've reached the end of the stream or filled the buffer
+            while (this.currentDataRemaining == 0 && bytesRead < count)
+            {
+                this.currentDataRemaining = this.getData();
+
+                if (this.currentDataRemaining == 0)
+                {
+                    return bytesRead;
+                }
+
+                offset += bytesRead;
+                bytesToRead = Math.Min(count - bytesRead, this.currentDataRemaining);
+                this.currentDataRemaining -= bytesToRead;
+                bytesRead += this.innerStream.Read(buffer, offset, bytesToRead);
+            }
+
+            return bytesRead;
         }
 
         /// <inheritdoc/>
@@ -165,14 +179,6 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
                 {
                     this.compressedStream.Dispose();
                     this.compressedStream = null;
-
-                    if (!this.crcRead)
-                    {
-                        // Consume the trailing 4 bytes
-                        this.innerStream.Read(ChecksumBuffer, 0, 4);
-                        this.currentDataRemaining -= 4;
-                        this.crcRead = true;
-                    }
                 }
             }