Fix #114848: Crash when adding specular texture slot in texture paint mode

This is because the idname for specular node is changed in 1d265eed5d.
Hence `nodeFindSocket` was returning invalid socket.

Pull Request: https://projects.blender.org/blender/blender/pulls/114884

source/blender/editors/sculpt_paint/paint_image_proj.cc

@@ -6512,7 +6512,7 @@ enum {
 
 static const EnumPropertyItem layer_type_items[] = {
     {LAYER_BASE_COLOR, "BASE_COLOR", 0, "Base Color", ""},
-    {LAYER_SPECULAR, "SPECULAR", 0, "Specular", ""},
+    {LAYER_SPECULAR, "SPECULAR", 0, "Specular IOR Level", ""},
     {LAYER_ROUGHNESS, "ROUGHNESS", 0, "Roughness", ""},
     {LAYER_METALLIC, "METALLIC", 0, "Metallic", ""},
     {LAYER_NORMAL, "NORMAL", 0, "Normal", ""},