Prevent infinite loop if the default FontFamily lookup fails

src/Avalonia.Base/Media/FontManager.cs

@@ -151,8 +151,13 @@ namespace Avalonia.Media
                 }
             }
 
+            if(typeface.FontFamily == DefaultFontFamily)
+            {
+                return false;
+            }
+
             //Nothing was found so use the default
-            return TryGetGlyphTypeface(new Typeface(DefaultFontFamily, typeface.Style, typeface.Weight, typeface.Stretch), out glyphTypeface);
+            return TryGetGlyphTypeface(new Typeface(FontFamily.DefaultFontFamilyName, typeface.Style, typeface.Weight, typeface.Stretch), out glyphTypeface);
         }
 
         /// <summary>

tests/Avalonia.Skia.UnitTests/Media/FontManagerTests.cs

@@ -123,5 +123,21 @@ namespace Avalonia.Skia.UnitTests.Media
                 }
             }
         }
+
+        [Fact]
+        public void Should_Return_False_For_Invalid_DefaultFontFamily()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface.With(fontManagerImpl: new FontManagerImpl())))
+            {
+                using (AvaloniaLocator.EnterScope())
+                {
+                    AvaloniaLocator.CurrentMutable.BindToSelf(new FontManagerOptions { DefaultFamilyName = "ABC" });
+
+                    var result = FontManager.Current.TryGetGlyphTypeface(Typeface.Default, out _);
+
+                    Assert.False(result);
+                }
+            }
+        }
     }
 }