NetworkPkg: Replace ASSERT with error handling in Http boot and IScsi

v2:
*Fix some memory leak issue.

This patch is used to replace ASSERT with error handling in Http boot
Driver and IScsi driver.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Zhang Lubo <lubo.zhang@intel.com>
Reviewed-By: Wu Jiaxin <jiaxin.wu@intel.com>

NetworkPkg/IScsiDxe/IScsiConfig.c

@@ -1987,7 +1987,11 @@ IScsiFormExtractConfig (
     ConfigRequestHdr = HiiConstructConfigHdr (&gIScsiConfigGuid, mVendorStorageName, Private->DriverHandle);
     Size = (StrLen (ConfigRequestHdr) + 32 + 1) * sizeof (CHAR16);
     ConfigRequest = AllocateZeroPool (Size);
-    ASSERT (ConfigRequest != NULL);
+    if (ConfigRequest == NULL) {
+      FreePool (IfrNvData);
+      FreePool (InitiatorName);
+      return EFI_OUT_OF_RESOURCES;
+    }
     AllocatedRequest = TRUE;
     UnicodeSPrint (ConfigRequest, Size, L"%s&OFFSET=0&WIDTH=%016LX", ConfigRequestHdr, (UINT64)BufferSize);
     FreePool (ConfigRequestHdr);