patch 8.1.2119: memory access error for empty string
Problem: memory access error for empty string when 'encoding' is a single
byte encoding.
Solution: Check for empty string when getting the length. (Dominique Pelle,
closes #5021, closes #5007)
diff --git a/src/macros.h b/src/macros.h
index d685dea..5e047c8 100644
--- a/src/macros.h
+++ b/src/macros.h
@@ -230,11 +230,11 @@
* PTR2CHAR(): get character from pointer.
*/
/* Get the length of the character p points to, including composing chars */
-#define MB_PTR2LEN(p) (has_mbyte ? (*mb_ptr2len)(p) : 1)
+#define MB_PTR2LEN(p) (has_mbyte ? (*mb_ptr2len)(p) : (*p == NUL ? 0 : 1))
/* Advance multi-byte pointer, skip over composing chars. */
-#define MB_PTR_ADV(p) p += has_mbyte ? (*mb_ptr2len)(p) : 1
+#define MB_PTR_ADV(p) p += has_mbyte ? (*mb_ptr2len)(p) : (*p == NUL ? 0 : 1)
/* Advance multi-byte pointer, do not skip over composing chars. */
-#define MB_CPTR_ADV(p) p += enc_utf8 ? utf_ptr2len(p) : has_mbyte ? (*mb_ptr2len)(p) : 1
+#define MB_CPTR_ADV(p) p += enc_utf8 ? utf_ptr2len(p) : has_mbyte ? (*mb_ptr2len)(p) : (*p == NUL ? 0 : 1)
/* Backup multi-byte pointer. Only use with "p" > "s" ! */
#define MB_PTR_BACK(s, p) p -= has_mbyte ? ((*mb_head_off)(s, p - 1) + 1) : 1
/* get length of multi-byte char, not including composing chars */