Auto merge of servo#6118 - Ryman:gh5856, r=pcwalton

Fixes servo#5856 

This stops the panic, but the empty fragments tend to be non-empty if extended by `info.range_end_including_stripped_whitespace`, so I'm unsure if it's a requirement to include that instead of skipping for correctness? Perhaps there's a testcase needed for this behaviour?

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components/layout/inline.rs

@@ -959,14 +959,13 @@ impl InlineFlow {
  let mut expansion_opportunities = 0i32;
  for fragment_index in line.range.each_index() {
  let fragment = fragments.get(fragment_index.to_usize());
- let scanned_text_fragment_info =
- if let SpecificFragmentInfo::ScannedText(ref info) = fragment.specific {
- info
- } else {
- continue
- };
- for slice in scanned_text_fragment_info.run.character_slices_in_range(
- &scanned_text_fragment_info.range) {
+ let scanned_text_fragment_info = match fragment.specific {
+ SpecificFragmentInfo::ScannedText(ref info) if !info.range.is_empty() => info,
+ _ => continue
+ };
+ let fragment_range = scanned_text_fragment_info.range;
+
+ for slice in scanned_text_fragment_info.run.character_slices_in_range(&fragment_range) {
  expansion_opportunities += slice.glyphs.space_count_in_range(&slice.range) as i32
  }
  }
@@ -976,12 +975,10 @@ impl InlineFlow {
  (expansion_opportunities as f64);
  for fragment_index in line.range.each_index() {
  let fragment = fragments.get_mut(fragment_index.to_usize());
- let mut scanned_text_fragment_info =
- if let SpecificFragmentInfo::ScannedText(ref mut info) = fragment.specific {
- info
- } else {
- continue
- };
+ let mut scanned_text_fragment_info = match fragment.specific {
+ SpecificFragmentInfo::ScannedText(ref mut info) if !info.range.is_empty() => info,
+ _ => continue
+ };
  let fragment_range = scanned_text_fragment_info.range;
 
  // FIXME(pcwalton): This is an awful lot of uniqueness making. I don't see any easy way