patch 8.0.0544: cppcheck warnings

Problem:    Cppcheck warnings.
Solution:   Use temp variable. Change NUL to NULL. Swap conditions. (Dominique
            Pelle)

src/channel.c

@@ -2571,9 +2571,14 @@ may_invoke_callback(channel_T *channel, ch_part_T part)
 	    if (nl == NULL)
 	    {
 		/* Flush remaining message that is missing a NL. */
-		buf = vim_realloc(buf, node->rq_buflen + 1);
-		if (buf == NULL)
+		char_u	*new_buf;
+
+		new_buf = vim_realloc(buf, node->rq_buflen + 1);
+		if (new_buf == NULL)
+		    /* This might fail over and over again, should the message
+		     * be dropped? */
 		    return FALSE;
+		buf = new_buf;
 		node->rq_buffer = buf;
 		nl = buf + node->rq_buflen++;
 		*nl = NUL;

src/edit.c

@@ -9524,7 +9524,7 @@ bracketed_paste(paste_mode_T mode, int drop, garray_T *gap)
 #endif
 	    buf[idx++] = c;
 	buf[idx] = NUL;
-	if (end != NUL && STRNCMP(buf, end, idx) == 0)
+	if (end != NULL && STRNCMP(buf, end, idx) == 0)
 	{
 	    if (end[idx] == NUL)
 		break; /* Found the end of paste code. */

src/farsi.c

@@ -1695,7 +1695,7 @@ conv_to_pvim(void)
 		ptr[i] = toF_leading(ptr[i]);
 		++i;
 
-		while (canF_Rjoin(ptr[i]) && i < llen)
+		while (i < llen && canF_Rjoin(ptr[i]))
 		{
 		    ptr[i] = toF_Rjoin(ptr[i]);
 		    if (F_isterm(ptr[i]) || !F_isalpha(ptr[i]))

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    544,
 /**/
     543,
 /**/