Pressing Up while on the first line should move cursor to (0,0)

Originally from CodeMirror:

    From 4ec8a344b55de67142ebe3143df8ac55e2e4f32e Mon Sep 17 00:00:00 2001
    From: Pavel Feldman <[e-mail]>
    Date: Tue, 7 Aug 2012 10:52:24 +0400
    Subject: [PATCH] Pressing Up while on the first line should move cursor to
     (0,0)

IPython/frontend/html/notebook/static/codemirror/README-IPython.rst

@@ -7,6 +7,10 b' is (*please update this information when updating versions*)::'
 
     CodeMirror2 4e244d252a26a2dba5446d44eb46adfb3c7f356a , tag : v2.32
 
+The following CodeMirror commits have been cherry-picked into the source:
+
+  * 4ec8a34 Pressing Up while on the first line should move cursor to (0,0)
+
 The current politics is not to ships the following folders of CodeMirrors :
 
   * doc/

IPython/frontend/html/notebook/static/codemirror/lib/codemirror.js

@@ -1738,7 +1738,7 b' var CodeMirror = (function() {'
     }
     // Coords must be lineSpace-local
     function coordsChar(x, y) {
-      if (y < 0) y = 0;
+      if (y < 0) return {line: 0, ch: 0};
       var th = textHeight(), cw = charWidth(), heightPos = displayOffset + Math.floor(y / th);
       var lineNo = lineAtHeight(doc, heightPos);
       if (lineNo >= doc.size) return {line: doc.size - 1, ch: getLine(doc.size - 1).text.length};