MdeModulePkg DxeCapsuleLibFmp: Update SupportCapsuleImage() for Fake Capsule

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1088
Per UEFI spec, the fake capsule image with the header only is a valid case
in QueryCapsuleCpapbilities(). So, SupportCapsuleImage() is updated to
support this case.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Liming Gao <liming.gao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>

MdeModulePkg/Library/DxeCapsuleLibFmp/DxeCapsuleLib.c

@@ -1421,6 +1421,12 @@ SupportCapsuleImage (
   }
 
   if (IsFmpCapsule(CapsuleHeader)) {
+    //
+    // Fake capsule header is valid case in QueryCapsuleCpapbilities().
+    //
+    if (CapsuleHeader->HeaderSize == CapsuleHeader->CapsuleImageSize) {
+      return EFI_SUCCESS;
+    }
     //
     // Check layout of FMP capsule
     //