patch 8.2.0943: displaying ^M or ^J depends on current buffer

Problem:    Displaying ^M or ^J depends on current buffer.
Solution:   Pass the displayed buffer to transchar(). (closes #6225)

src/message.c

@@ -1752,7 +1752,7 @@ str2special(
 	// For multi-byte characters check for an illegal byte.
 	if (has_mbyte && MB_BYTE2LEN(*str) > len)
 	{
-	    transchar_nonprint(buf, c);
+	    transchar_nonprint(curbuf, buf, c);
 	    *sp = str + 1;
 	    return buf;
 	}