Update font size checks in Syntax Highlighter preferences

Syntax Highlighter tab of Preferences dialogue box now checks that
entered font sizes are within the range of common font sizes and
displays an error where they are not.

Author: delphidabbler

Src/FrHiliterPrefs.pas

@@ -215,6 +215,8 @@ implementation
 
   // Error messages
   sErrBadFontSize       = 'Invalid font size';
+  sErrBadFontRange      = 'Font size out of range. '
+                          + 'Enter a value between %0:d and %1:d';
 
 const
   ///  <summary>Map of highlighter elements to descriptions.</summary>
@@ -342,10 +344,24 @@ procedure THiliterPrefsFrame.cbFontSizeChange(Sender: TObject);
     Exit;
   if TryStrToInt(cbFontSize.Text, Size) then
   begin
-    // Combo has valid value entered: update
-    fAttrs.FontSize := Size;
-    UpdatePreview;
-    fChanged := True;
+    if TFontHelper.IsInCommonFontSizeRange(Size) then
+    begin
+      // Combo has valid value entered: update
+      fAttrs.FontSize := Size;
+      UpdatePreview;
+      fChanged := True;
+    end
+    else
+    begin
+      TMessageBox.Error(
+        ParentForm,
+        Format(
+          sErrBadFontRange,
+          [TFontHelper.CommonFontSizes.Min, TFontHelper.CommonFontSizes.Max]
+        )
+      );
+      cbFontSize.Text := IntToStr(fAttrs.FontSize);
+    end;
   end
   else
   begin