patch 8.0.1014: old compiler doesn't know uint32_t

Problem:    Old compiler doesn't know uint32_t. Warning for using NULL instead
            of NUL.
Solution:   Use UINT32_T.  Use NUL instead of NULL.
diff --git a/src/proto/mbyte.pro b/src/proto/mbyte.pro
index b37064b..44fcfc5 100644
--- a/src/proto/mbyte.pro
+++ b/src/proto/mbyte.pro
@@ -10,7 +10,7 @@
 int latin_char2bytes(int c, char_u *buf);
 int latin_ptr2len(char_u *p);
 int latin_ptr2len_len(char_u *p, int size);
-int utf_uint2cells(uint32_t c);
+int utf_uint2cells(UINT32_T c);
 int utf_char2cells(int c);
 int latin_ptr2cells(char_u *p);
 int utf_ptr2cells(char_u *p);
@@ -38,7 +38,7 @@
 int utfc_ptr2len_len(char_u *p, int size);
 int utf_char2len(int c);
 int utf_char2bytes(int c, char_u *buf);
-int utf_iscomposing_uint(uint32_t c);
+int utf_iscomposing_uint(UINT32_T c);
 int utf_iscomposing(int c);
 int utf_printable(int c);
 int utf_class(int c);