Catch exceptions in cursor detection.

If cursor Data URI scheme detection threw an exception, it would cause
canvas initialization to fail. cursor detection exceptions should just
disable local cursor change support, not cause canvas init to fail.

include/canvas.js

@@ -194,6 +194,7 @@ init: function (id) {
     for (i=0; i < 8 * 8 * 4; i++) {
         curDat.push(255);
     }
+    try {
         curSave = c.style.cursor;
         Canvas.changeCursor(curDat, curDat, 2, 2, 8, 8);
         if (c.style.cursor) {
@@ -203,6 +204,10 @@ init: function (id) {
             Util.Warn("Data URI scheme cursor not supported");
         }
         c.style.cursor = curSave;
+    } catch (exc2) {
+        Util.Error("Data URI scheme cursor test exception: " + exc2);
+        conf.cursor_uri = false;
+    }
 
     Canvas.colourMap = [];
     Canvas.prevStyle = "";