fix infinite loop

(and this, kids, is why oneliners loops are inherently suspicious)

(cherry picked from commit 727f6e3ef4533effcdc77e943f04e3c6b134cd1e)

libraries/lib-label-track/LabelTrack.cpp

@@ -523,8 +523,11 @@ LabelStruct LabelStruct::Import(wxTextFile &file, int &index, LabelFormat format
       // Labels in audacity should be only one line, so join multiple lines
       // with spaces.  This is not reversed on export.
       while (index < (int)file.GetLineCount() &&
-             !file.GetLine(index).IsEmpty())
+             !file.GetLine(index).IsEmpty()) 
+      {
          title += " " + file.GetLine(index);
+         index++;
+      }
 
       index++; // Skip over empty line