Fix mbstowcs_nonfatal() that might convert string shorter than desired

The "n" parameter of mbstowcs_nonfatal() refers to number of wide
characters. But the logic seemed to be confused with "n" parameter of
mbrtowc() (the number of bytes).

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

Author: Explorer09

RichString.c

@@ -12,6 +12,7 @@ in the source distribution for its full text.
 #include <assert.h>
 #include <ctype.h>
 #include <limits.h> // IWYU pragma: keep
+#include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
@@ -69,16 +70,15 @@ static size_t mbstowcs_nonfatal(wchar_t* restrict dest, const char* restrict src
    mbstate_t ps = { 0 };
    bool broken = false;
 
-   while (n > 0) {
-      size_t ret = mbrtowc(dest, src, n, &ps);
+   while (written < n) {
+      size_t ret = mbrtowc(dest, src, SIZE_MAX, &ps);
       if (ret == (size_t)-1 || ret == (size_t)-2) {
          if (!broken) {
             broken = true;
             *dest++ = L'\xFFFD';
             written++;
          }
          src++;
-         n--;
          continue;
       }
 
@@ -91,7 +91,6 @@ static size_t mbstowcs_nonfatal(wchar_t* restrict dest, const char* restrict src
       dest++;
       written++;
       src += ret;
-      n -= ret;
    }
 
    return written;