Fix MaybeRel when OUT is absolute

MaybeRel was failing with an error when comparing an absolute out
path to a relative source path.  Make it return false instead, and
add tests.

Bug: 119412419
Test: paths_test.go
Change-Id: I462182638bd57b1367b5bfb0718e975c11ae66f7

android/paths.go

@@ -1054,6 +1054,10 @@ func Rel(ctx PathContext, basePath string, targetPath string) string {
 // MaybeRel performs the same function as filepath.Rel, but reports errors to a PathContext, and returns false if
 // targetPath is not inside basePath.
 func MaybeRel(ctx PathContext, basePath string, targetPath string) (string, bool) {
+	// filepath.Rel returns an error if one path is absolute and the other is not, handle that case first.
+	if filepath.IsAbs(basePath) != filepath.IsAbs(targetPath) {
+		return "", false
+	}
 	rel, err := filepath.Rel(basePath, targetPath)
 	if err != nil {
 		reportPathError(ctx, err)