Make sure gutters are never left higher than the view height

Closes codemirror#3884

Author: marijnh

lib/codemirror.js

@@ -747,6 +747,7 @@
 
   function postUpdateDisplay(cm, update) {
     var viewport = update.viewport;
+
     for (var first = true;; first = false) {
       if (!first || !cm.options.lineWrapping || update.oldDisplayWidth == displayWidth(cm)) {
         // Clip forced viewport to actual scrollable area.
@@ -766,6 +767,9 @@
       updateScrollbars(cm, barMeasure);
     }
 
+    if (parseInt(cm.display.gutters.style.height) > cm.display.scroller.clientHeight)
+      cm.display.gutters.style.height = cm.display.scroller.clientHeight + "px"
+
     update.signal(cm, "update", cm);
     if (cm.display.viewFrom != cm.display.reportedViewFrom || cm.display.viewTo != cm.display.reportedViewTo) {
       update.signal(cm, "viewportChange", cm, cm.display.viewFrom, cm.display.viewTo);