user32: Pre-allocate the window procedure for the dialog class.

dlls/user32/controls.h

@@ -35,6 +35,7 @@ enum builtin_winprocs
 {
     WINPROC_BUTTON = 0,
     WINPROC_COMBO,
+    WINPROC_DIALOG,
     WINPROC_EDIT,
     WINPROC_LISTBOX,
     WINPROC_SCROLLBAR,

dlls/user32/dialog.c

@@ -97,8 +97,8 @@ const struct builtin_class_descr DIALOG_builtin_class =
 {
     (LPCWSTR)DIALOG_CLASS_ATOM, /* name */
     CS_SAVEBITS | CS_DBLCLKS, /* style  */
-    DefDlgProcA,        /* procA */
-    DefDlgProcW,        /* procW */
+    NULL,               /* procA */
+    BUILTIN_WINPROC(WINPROC_DIALOG), /* procW */
     DLGWINDOWEXTRA,     /* extra */
     IDC_ARROW,          /* cursor */
     0                   /* brush */

dlls/user32/winproc.c

@@ -66,6 +66,7 @@ static WINDOWPROC winproc_array[MAX_WINPROCS] =
 {
     { ButtonWndProcA, ButtonWndProcW },        /* WINPROC_BUTTON */
     { ComboWndProcA, ComboWndProcW },          /* WINPROC_COMBO */
+    { DefDlgProcA, DefDlgProcW },              /* WINPROC_DIALOG */
     { EditWndProcA, EditWndProcW },            /* WINPROC_EDIT */
     { ListBoxWndProcA, ListBoxWndProcW },      /* WINPROC_LISTBOX */
     { ScrollBarWndProcA, ScrollBarWndProcW },  /* WINPROC_SCROLLBAR */