Remove redundant bounds check for lookup in BIG5 conversion table

For CP950 conversion, the bounds check is needed before doing a lookup
in big5_ucs_table, since the first byte of a CP950 multibyte
character can be up to 0xFE. For BIG5, we only accept 1st bytes up
to 0xF9, and it is not possible for the lookup to go out of bounds.

Author: alexdowad

ext/mbstring/libmbfl/filters/mbfilter_big5.c

@@ -400,8 +400,9 @@ static size_t mb_big5_to_wchar(unsigned char **in, size_t *in_len, uint32_t *buf
 			unsigned char c2 = *p++;
 
 			if ((c2 >= 0x40 && c2 <= 0x7E) || (c2 >= 0xA1 && c2 <= 0xFE)) {
-				unsigned int w = ((c - 0xA1)*157) + c2 - ((c2 <= 0x7E) ? 0x40 : 0xA1 - 0x3F);
-				w = (w < big5_ucs_table_size) ? big5_ucs_table[w] : 0;
+				unsigned int w = (c - 0xA1)*157 + c2 - ((c2 <= 0x7E) ? 0x40 : 0xA1 - 0x3F);
+				ZEND_ASSERT(w < big5_ucs_table_size);
+				w = big5_ucs_table[w];
 				if (!w)
 					w = MBFL_BAD_INPUT;
 				*out++ = w;