e: double paranthesis as gcc suggests

Since we assign and check for true value in one operation, use double
paranthesis.

src/bin/e_actions.c

@@ -829,7 +829,7 @@ ACT_FN_GO(window_border_cycle, __UNUSED__)
                {
                   const char *bdname = params;
 
-                  while (space = strchr(bdname, ' '))
+                  while ((space = strchr(bdname, ' ')))
                     {
                        if (strncmp(bd->bordername, bdname, space - bdname) == 0)
                          {