Filter empty sub-paths

[brawer]

For test case SHARAN-1, the test suite reports a test failure for CoreText on macOS 10.14 but the rendered path looks fine. For example, the first path in the test expectation, which was generated by HarfBuzz and FreeType, has the following delta to CoreText; note that the final moveto in the test expecation is a no-op because it is immediately followed by closepath.

--- expected
+++ CoreText
@@ -1,2 +1 @@
-<path d="M-86,203 L-86,211 Q-74,230 -43,265 Q-12,299 0,307 L8,307 Q46,283 66,263 Q86,243 86,223 Q86,187 4,128 L-4,128 Q-46,171 -86,203 Z M0,217 Z" />
-
+<path d="M-86,203 L-86,211 Q-74,230 -43,265 Q-12,299 0,307 L8,307 Q46,283 66,263 Q86,243 86,223 Q86,187 4,128 L-4,128 Q-46,171 -86,203 Z" />

To fix, we probably should change the test runner to filter out empty sub-paths.