Revert "Minor"

This reverts commit 3e0a0397.

I know remember why that line is there :).

src/hb-ot-shape-complex-arabic.cc

@@ -90,6 +90,7 @@ static hb_codepoint_t get_arabic_shape (hb_codepoint_t u, unsigned int shape)
 
 static uint16_t get_ligature (hb_codepoint_t first, hb_codepoint_t second)
 {
+  if (unlikely (!second)) return 0;
   for (unsigned i = 0; i < ARRAY_LENGTH (ligature_table); i++)
     if (ligature_table[i].first == first)
       for (unsigned j = 0; j < ARRAY_LENGTH (ligature_table[i].ligatures); j++)