Correct misdetection of [001] as literal zero index

The control flow in expand.cpp is a bit more complicated than it seemed
at first blush. Ref #4862.

src/expand.cpp

@@ -260,6 +260,7 @@ static size_t parse_slice(const wchar_t *in, wchar_t **end_ptr, std::vector<long
         }
 
         // debug( 0, L"Push idx %d", tmp );
+        literal_zero_index = literal_zero_index && tmp == 0;
         idx.push_back(i1);
         source_positions.push_back(i1_src_pos);
     }

tests/zero_based_array.in

@@ -1,3 +1,8 @@
 echo $foo[0]
 echo $foo[ 0 ]
 echo $foo[ 00 ]
+
+# and make sure these didn't break
+set -l foo one two three
+echo $foo[001]
+

tests/zero_based_array.out

@@ -0,0 +1 @@
+one