BaseTools ConvertMasmToNasm: Don't try to reconvert .nasm files

We now check to see if the destination .nasm file already exists. If
it does, then we don't try to convert the .asm to .nasm.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Scripts/ConvertMasmToNasm.py

@@ -768,7 +768,8 @@ class ConvertInfFile(CommonUtils):
                 src = self.mo.group(1)
                 srcExt = self.mo.group(2)
                 dst = os.path.splitext(src)[0] + '.nasm'
-                if src not in srcToDst:
+                fullDst = os.path.join(self.dir, dst)
+                if src not in srcToDst and not os.path.exists(fullDst):
                     srcToDst[src] = dst
                     srcToDst['order'].append(src)
         return srcToDst