build/bazel_cc_fix: ignore files not found

Otherwise it could end up rewriting valid system includes it could not
find (for example because they are part of the compiler) into includes
with empty path.

Change-Id: Ia34cecacf7c863d106924080920c98fff72dba3a
Reviewed-on: https://review.monogon.dev/c/monogon/+/3344
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/build/bazel_cc_fix/main.go b/build/bazel_cc_fix/main.go
index b115e50..4292b0d 100644
--- a/build/bazel_cc_fix/main.go
+++ b/build/bazel_cc_fix/main.go
@@ -209,6 +209,9 @@
 			workspaceRelativeFilePath = findFileInWorkspace(searchPath, inclFile, isGeneratedFile)
 		}
 		workspaceRelativeFilePath = applyReplaceDirectives(spec.Replace, ccfixspec.Replace_WORKSPACE, workspaceRelativeFilePath, true)
+		if workspaceRelativeFilePath == "" {
+			continue
+		}
 
 		// Mark generated files as generated
 		foundGenerated := isGeneratedFile[filepath.Join(*workspacePath, workspaceRelativeFilePath)]