Fix T92636: Vector math node link disconnects when loading old file

Previously, unique identifiers for sockets were created automatically,
sometimes using .001 and sometimes _001. Now they are created
manually with the second format, but some files were saved with .001
format. I think this was only an issue in the vector math node.

rBd845ba481c6d fixed this problem in 3.1, but in a more general way.
After I merge this patch to 3.1, I will revert it, since the versioning
added in that commit will make this redundant.

Differential Revision: https://developer.blender.org/D13209

source/blender/blenloader/intern/versioning_300.c

@@ -783,7 +783,6 @@ void do_versions_after_linking_300(Main *bmain, ReportList *UNUSED(reports))
    */
   {
     /* Keep this block, even when empty. */
-
   }
 }
 
@@ -2159,6 +2158,20 @@ void blo_do_versions_300(FileData *fd, Library *UNUSED(lib), Main *bmain)
    * \note Keep this message at the bottom of the function.
    */
   {
-    /* Keep this block, even when empty. */
+    /* Use consistent socket identifiers for the vector math node.
+     * Thecode to make unique identifiers from the names was inconsitent. */
+    FOREACH_NODETREE_BEGIN (bmain, ntree, id) {
+      if (ELEM(ntree->type, NTREE_SHADER, NTREE_GEOMETRY)) {
+        LISTBASE_FOREACH (bNode *, node, &ntree->nodes) {
+          if (node->type == SH_NODE_MATH) {
+            bNodeSocket *value1 = ((bNodeSocket *)node->inputs.first)->next;
+            bNodeSocket *value2 = value1->next;
+            strcpy(value1->identifier, "Value_001");
+            strcpy(value2->identifier, "Value_002");
+          }
+        }
+      }
+    }
+    FOREACH_NODETREE_END;
   }
 }