[Mac] Fix NRE on setting non-existing FontFamily (#7636) fixes #7582

* Update FontExtensions.cs

* Added issue to gallery

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7582.cs

@@ -0,0 +1,24 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 7582, "Null Reference Exception thrown when set FontFamily for label in Xamarin Forms macOS", PlatformAffected.macOS)]
+	public class Issue7582 : TestContentPage
+	{
+		protected override void Init()
+		{
+			var label = new Label
+			{
+				Text = "This is a label with a non-existent FontFamily, If you're seeing this label the test succeeded.",
+				FontFamily = "THISISNOTAFONT",
+				FontAttributes = FontAttributes.Bold,
+				VerticalOptions = LayoutOptions.Center,
+				HorizontalOptions = LayoutOptions.Center
+			};
+
+			Content = label;
+		}
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -1023,6 +1023,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue6894.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue6929.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Controls\ApiLabel.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue7582.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">

Xamarin.Forms.Platform.MacOS/Extensions/FontExtensions.cs

@@ -38,7 +38,10 @@ namespace Xamarin.Forms.Platform.MacOS
 
 			//if we didn't found a Font or Descriptor for the FontFamily use the default one 
 			if (font == null)
+			{
 				font = defaultFont;
+				descriptor = defaultFont.FontDescriptor;
+			}
 		
 			if (descriptor == null)
 				descriptor = defaultFont.FontDescriptor;
@@ -47,16 +50,16 @@ namespace Xamarin.Forms.Platform.MacOS
 			{
 				var traits = (NSFontSymbolicTraits)0;
 				if (bold)
-					traits = traits | NSFontSymbolicTraits.BoldTrait;
+					traits |= NSFontSymbolicTraits.BoldTrait;
 				if (italic)
-					traits = traits | NSFontSymbolicTraits.ItalicTrait;
+					traits |= NSFontSymbolicTraits.ItalicTrait;
 
-				var fontDescriptoWithTraits = descriptor.FontDescriptorWithSymbolicTraits(traits);
+				var fontDescriptorWithTraits = descriptor.FontDescriptorWithSymbolicTraits(traits);
 
-				font = NSFont.FromDescription(fontDescriptoWithTraits, size);
+				font = NSFont.FromDescription(fontDescriptorWithTraits, size);
 			}
 
 			return font.ScreenFontWithRenderingMode(NSFontRenderingMode.AntialiasedIntegerAdvancements);
 		}
 	}
-}
+}