This patch fixes |ShapeResult::CopyRanges| when there are no
runs.

|CopyRangeInternal| sets |num_characters_| and |start_index_|
when there are no glyphs to copy. The early return in
|CopyRanges| preents setting these fields when there are no
runs in the source |ShapeResult|.

Incorrect |num_characters_| and |start_index_| can crash
|NGLineBreaker| and/or |ShapingLineBreaker|.

Note, missing glyphs and missing runs are hard to reproduce
in tests across platforms that the test in this patch creates
such |ShapeResult| artificially.

Bug: 963521
Change-Id: Id7cad35816ac18df1add75d2d30bb09676ed5f39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1822397
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699550}