deploy-rbutil.py: allow zipball building to proceed if no DLLs are found

This helps with MXE static builds, which were failing because no DLLs were
found.

Change-Id: Id3fcdf9a7682a9ecb6a5892415077bf16e8b24cb

utils/common/deploy.py

@@ -347,7 +347,7 @@ def zipball(programfiles, versionstring, buildfolder, platform=sys.platform):
     for f in programfiles:
         if re.match(r'^(/|[a-zA-Z]:)', f) != None:
             shutil.copy(f, outfolder)
-        else:
+        elif len(f) > 0:
             shutil.copy(buildfolder + "/" + f, outfolder)
     # create zipball from output folder
     zf = zipfile.ZipFile(archivename, mode='w', compression=zipfile.ZIP_DEFLATED)