NetworkPkg/HttpBootDxe: Avoid the potential memory leak when eror happen.

Cc: Wang Fan <fan.wang@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Wang Fan <fan.wang@intel.com>

NetworkPkg/HttpBootDxe/HttpBootImpl.c

@@ -122,8 +122,9 @@ HttpBootStart (
   UINTN                Index;
   EFI_STATUS           Status;
   CHAR8                *Uri;
-  
 
+  Uri = NULL;
+  
   if (Private == NULL || FilePath == NULL) {
     return EFI_INVALID_PARAMETER;
   }
@@ -154,6 +155,9 @@ HttpBootStart (
       //
       Status = HttpBootStop (Private);
       if (EFI_ERROR (Status)) {
+        if (Uri != NULL) {
+          FreePool (Uri);
+        }
         return Status;
       }
     } else {