Fix error on empty regex text

Source/Editor/Windows/OutputLogWindow.cs

@@ -551,6 +551,8 @@ namespace FlaxEditor.Windows
                             if (j == 0)
                                 regexStart += prefixLength;
                             var regexLength = line.LastCharIndex - regexStart;
+                            if (regexLength > 0)
+                            {
                                 var match = _compileRegex.Match(entryText, regexStart, regexLength);
                                 if (match.Success)
                                 {
@@ -573,6 +575,7 @@ namespace FlaxEditor.Windows
                                 // TODO: parsing hyperlinks with link
                                 // TODO: parsing file paths with link
                             }
+                        }
 
                         prevBlockBottom += line.Size.Y;
                         _textBlocks.Add(textBlock);