diff: check range before dereferencing an array element

Before accessing an array element at a given index, we should make sure
that the index is within the desired bounds, not afterwards, otherwise
it may not make sense to even access the array element in the first
place.

Pointed out by CodeQL's `cpp/offset-use-before-range-check` rule.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

diff.c

@@ -892,7 +892,7 @@ static void fill_es_indent_data(struct emitted_diff_symbol *es)
 
 	/* skip any \v \f \r at start of indentation */
 	while (s[off] == '\f' || s[off] == '\v' ||
-	       (s[off] == '\r' && off < len - 1))
+	       (off < len - 1 && s[off] == '\r'))
 		off++;
 
 	/* calculate the visual width of indentation */