Clip offsets returned from caretPositionFromPoint

FIX: Work around odd behavior in Chrome's newly supported `caretPositionFromPoint`
method, which could cause CodeMirror to crash with a null dereference.

src/cursor.ts

@@ -4,7 +4,7 @@ import {EditorView} from "./editorview"
 import {BlockType} from "./decoration"
 import {LineView} from "./blockview"
 import {atomicRanges} from "./extension"
-import {clientRectsFor, textRange, Rect} from "./dom"
+import {clientRectsFor, textRange, Rect, maxOffset} from "./dom"
 import {moveVisually, movedOver, Direction} from "./bidi"
 import {BlockInfo} from "./heightmap"
 import browser from "./browser"
@@ -184,6 +184,10 @@ export function posAtCoords(view: EditorView, coords: {x: number, y: number}, pr
           node = undefined
       }
     }
+    // Chrome will return offsets into <input> elements without child
+    // nodes, which will lead to a null deref below, so clip the
+    // offset to the node size.
+    if (node) offset = Math.min(maxOffset(node), offset)
   }
 
   // No luck, do our own (potentially expensive) search