Speed up connection matching. Fix theoretical race condition.

core/connection.js

@@ -527,14 +527,14 @@ Blockly.Connection.prototype.closest = function(maxLimit, dx, dy) {
     } while (targetSourceBlock);
 
     // Only connections within the maxLimit radius.
-    var dx = currentX - db[yIndex].x_;
-    var dy = currentY - db[yIndex].y_;
+    var dx = currentX - connection.x_;
+    var dy = currentY - connection.y_;
     var r = Math.sqrt(dx * dx + dy * dy);
     if (r <= maxLimit) {
-      closestConnection = db[yIndex];
+      closestConnection = connection;
       maxLimit = r;
     }
-    return dy < maxLimit;
+    return Math.abs(dy) < maxLimit;
   }
   return {connection: closestConnection, radius: maxLimit};
 };

core/xml.js

@@ -274,7 +274,9 @@ Blockly.Xml.domToBlock = function(workspace, xmlBlock, opt_reuseBlock) {
     // Populating the connection database may be defered until after the blocks
     // have renderend.
     setTimeout(function() {
-      topBlock.setConnectionsHidden(false);
+      if (topBlock.workspace) {  // Check that the block hasn't been deleted.
+        topBlock.setConnectionsHidden(false);
+      }
     }, 1);
     topBlock.updateDisabled();
     // Fire an event to allow scrollbars to resize.