Limit loop in scrollPosIntoView at 5 steps

To prevent infinite loops when the algorithm somehow doesn't converge

(It should converge, but infinite loops with nebulous termination
conditions are a rather bad source of hangs.)

I'm still torn about this, since it'll mask bugs.

Issue #2819

Author: marijnh

lib/codemirror.js

@@ -3721,7 +3721,7 @@
   // measured, the position of something may 'drift' during drawing).
   function scrollPosIntoView(cm, pos, end, margin) {
     if (margin == null) margin = 0;
-    for (;;) {
+    for (var limit = 0; limit < 5; limit++) {
       var changed = false, coords = cursorCoords(cm, pos);
       var endCoords = !end || end == pos ? coords : cursorCoords(cm, end);
       var scrollPos = calculateScrollPos(cm, Math.min(coords.left, endCoords.left),