patch 8.2.1128: the write message mentions characters, but it's bytes

Problem:    The write message mentions characters, but it's actually bytes.
Solution:   Change "C" to "B" and "characters" to "bytes".
diff --git a/src/fileio.c b/src/fileio.c
index 81a5026..e462310 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -3039,13 +3039,13 @@
 	*p++ = ' ';
     if (shortmess(SHM_LINES))
 	vim_snprintf((char *)p, IOSIZE - (p - IObuff),
-		"%ldL, %lldC", lnum, (varnumber_T)nchars);
+		"%ldL, %lldB", lnum, (varnumber_T)nchars);
     else
     {
 	sprintf((char *)p, NGETTEXT("%ld line, ", "%ld lines, ", lnum), lnum);
 	p += STRLEN(p);
 	vim_snprintf((char *)p, IOSIZE - (p - IObuff),
-		NGETTEXT("%lld character", "%lld characters", nchars),
+		NGETTEXT("%lld byte", "%lld bytes", nchars),
 		(varnumber_T)nchars);
     }
 }