Optimize out empty path components

filepath.Join("foo", "") returns a newly allocated copy of "foo",
while filepath.Join("foo") does not.  Strip out any empty path
components before calling filepath.Join.

Test: TestValidatePath
Change-Id: Ib47dbcd9d6463809acfe260dfd9af87ea280b4de
diff --git a/android/paths_test.go b/android/paths_test.go
index 2f87977..bf46c34 100644
--- a/android/paths_test.go
+++ b/android/paths_test.go
@@ -37,6 +37,22 @@
 		out: "",
 	},
 	{
+		in:  []string{"", ""},
+		out: "",
+	},
+	{
+		in:  []string{"a", ""},
+		out: "a",
+	},
+	{
+		in:  []string{"", "a"},
+		out: "a",
+	},
+	{
+		in:  []string{"", "a", ""},
+		out: "a",
+	},
+	{
 		in:  []string{"a/b"},
 		out: "a/b",
 	},