Fix UB nullptr passing to memcpy()

cutils.c

@@ -140,8 +140,10 @@ int dbuf_put(DynBuf *s, const uint8_t *data, size_t len)
         if (dbuf_realloc(s, s->size + len))
             return -1;
     }
+    if (len > 0) {
         memcpy(s->buf + s->size, data, len);
         s->size += len;
+    }
     return 0;
 }
 

libbf.c

@@ -292,6 +292,7 @@ int bf_set(bf_t *r, const bf_t *a)
     }
     r->sign = a->sign;
     r->expn = a->expn;
+    if (a->len > 0)
         memcpy(r->tab, a->tab, a->len * sizeof(limb_t));
     return 0;
 }

quickjs-libc.c

@@ -3462,6 +3462,7 @@ static JSValue js_worker_postMessage(JSContext *ctx, JSValueConst this_val,
     msg->sab_tab = malloc(sizeof(msg->sab_tab[0]) * sab_tab_len);
     if (!msg->sab_tab)
         goto fail;
+    if (sab_tab_len > 0)
         memcpy(msg->sab_tab, sab_tab, sizeof(msg->sab_tab[0]) * sab_tab_len);
     msg->sab_tab_len = sab_tab_len;
 

quickjs.c

@@ -32595,7 +32595,9 @@ static JSValue js_create_function(JSContext *ctx, JSFunctionDef *fd)
             }
         } else {
             b->vardefs = (void *)((uint8_t*)b + vardefs_offset);
+            if (fd->arg_count > 0)
                 memcpy(b->vardefs, fd->args, fd->arg_count * sizeof(fd->args[0]));
+            if (fd->var_count > 0)
                 memcpy(b->vardefs + fd->arg_count, fd->vars, fd->var_count * sizeof(fd->vars[0]));
         }
         b->var_count = fd->var_count;