dvec abstraction, #6/11, emphasise `v_plot = NULL' initialisation

src/frontend/define.c

@@ -171,7 +171,8 @@ savetree(struct pnode *pn)
             else
                 pn->pn_value->v_compdata = TMALLOC(ngcomplex_t, d->v_length);
 
-            pn->pn_value->v_plot = NULL; /* this dvec isn't member of any plot */
+            /* this dvec isn't member of any plot */
+
             if (isreal(d)) {
                 bcopy(d->v_realdata,
                       pn->pn_value->v_realdata,

src/frontend/dvec.c

@@ -12,6 +12,7 @@ dvec_alloc(void)
 
     ZERO(rv, struct dvec);
 
+    rv->v_plot = NULL;
     rv->v_numdims = 0;
 
     return rv;

src/frontend/parse.c

@@ -344,7 +344,6 @@ PP_mknnode(double number)
     v->v_flags = VF_REAL;
     v->v_realdata = TMALLOC(double, 1);
     v->v_length = 1;
-    v->v_plot = NULL;
 
     v->v_realdata[0] = number;