[overlay addon] Fix the `combine` option for overlay modes inside blankLines

addon/mode/overlay.js

@@ -76,8 +76,13 @@ CodeMirror.overlayMode = function(base, overlay, combine) {
     innerMode: function(state) { return {state: state.base, mode: base}; },
 
     blankLine: function(state) {
-      if (base.blankLine) base.blankLine(state.base);
-      if (overlay.blankLine) overlay.blankLine(state.overlay);
+      var baseToken, overlayToken;
+      if (base.blankLine) baseToken = base.blankLine(state.base);
+      if (overlay.blankLine) overlayToken = overlay.blankLine(state.overlay);
+
+      return overlayToken == null ?
+        baseToken :
+        (combine ? baseToken + " " + overlayToken : overlayToken);
     }
   };
 };