Fix handling of non-match highlight

In some cases, `git grep` will customize the foreground-color for more
than just the subset of the line that matches the grep pattern. This
breaks the current match-detection behavior, which considers any
characters with a non-default "foreground color" within the "code" part
of a git-grep-ouput-line to be part of the match. This commit makes
match-detection check for boldness and a red foreground instead of just
checking for a non-default foreground-color.

git grep matches are bold and red by default. But git grep isn't the
only reason input to delta may contain color codes; there may still be
cases where the highlighting looks wrong here.

src/handlers/grep.rs

@@ -232,7 +232,9 @@ fn get_code_style_sections<'b>(
         let match_style_sections = ansi::parse_style_sections(&raw_line[(prefix_end + 1)..])
             .iter()
             .map(|(ansi_term_style, s)| {
-                if ansi_term_style.foreground.is_some() {
+                if ansi_term_style.is_bold
+                    && ansi_term_style.foreground == Some(ansi_term::Colour::Red)
+                {
                     (match_style, *s)
                 } else {
                     (non_match_style, *s)
@@ -942,5 +944,18 @@ mod tests {
                 "kind: Service"
             )]))
         );
+
+        let plus_example = format!("etc/examples/189-merge-conflict.2.diff{escape}[36m:{escape}[m10{escape}[36m:{escape}[m{escape}[32m +        let (style, non_emph_style) = {escape}[1;31mmatch{escape}[m state {{{escape}[m");
+        let plus_stripped = strip_ansi_codes(&plus_example);
+        let plus_grep = parse_grep_line(&plus_stripped).unwrap();
+
+        assert_eq!(
+            get_code_style_sections(&plus_example, hit, miss, &plus_grep),
+            Some(StyleSectionSpecifier::StyleSections(vec![
+                (miss, " +        let (style, non_emph_style) = "),
+                (hit, "match"),
+                (miss, " state {")
+            ]))
+        );
     }
 }