Fix bug where two items could occupy same grid cell in hotseat.

When long pressing on an app to start, a drag would start on the
Workspace but mDragInfo would not be cleared since onDropCompleted
is not called in this case.

Solution is to set mDragInfo to null in onDragEnd.

Bug: 72206125
Change-Id: I2b9a1563c80e591d946a44f4e949b71f7b423a00
diff --git a/src/com/android/launcher3/Workspace.java b/src/com/android/launcher3/Workspace.java
index 8fb0e1c..2d24028 100644
--- a/src/com/android/launcher3/Workspace.java
+++ b/src/com/android/launcher3/Workspace.java
@@ -421,6 +421,7 @@
         }
 
         updateChildrenLayersEnabled();
+        mDragInfo = null;
         mOutlineProvider = null;
         mDragSourceInternal = null;
     }