[patch] Use a single log entry for MapCSS error logging

[gaben]

I noticed the issue when the edited MapCSS rule was invalid, see status report of #22878.

src/org/openstreetmap/josm/gui/mappaint/mapcss/MapCSSParser.jj

@@ -1162 +1162 @@
         e = new ParseException(pe.getMessage()); // prevent memory leak
     }
     
-    Logging.error("Skipping to the next rule, because of an error:");
-    Logging.error(e);
+    Logging.error("Skipping to the next rule, because of an error: " + e);
     if (sheet != null) {
         sheet.logError(e);
     }