make sure visibleLines doesn't return bogus range

Author: marijnh

lib/codemirror.js

@@ -604,7 +604,7 @@ var CodeMirror = (function() {
 
     function visibleLines() {
       var lh = lineHeight(), top = wrapper.scrollTop - paddingTop();
-      return {from: Math.max(0, Math.floor(top / lh)),
+      return {from: Math.min(lines.length, Math.max(0, Math.floor(top / lh))),
               to: Math.min(lines.length, Math.ceil((top + wrapper.clientHeight) / lh))};
     }
     // Uses a set of changes plus the current scroll position to
@@ -1043,7 +1043,7 @@ var CodeMirror = (function() {
     function lineHeight() {
       var nlines = lineDiv.childNodes.length;
       if (nlines) return lineDiv.offsetHeight / nlines;
-      else return measure.offsetHeight || 1;
+      else return measure.firstChild.offsetHeight || 1;
     }
     function charWidth() {return (measure.firstChild.offsetWidth || 320) / 40;}
     function paddingTop() {return lineSpace.offsetTop;}