Fix for #1706 (Wavk again!)

- Undo in texteditor didnt work, event (ALT+U) was swallowed by new undo
  menu (ALT+U too)
- global undo doesnt restore UI's as we know... so undo-ing with a text
  editor active cannot always restore correct text block you were editing.
  As extra service I added that when no restore is possible, it links to
  the first block available.

source/blender/blenloader/intern/readfile.c

@@ -2753,6 +2753,7 @@ void lib_link_screen_restore(Main *newmain, char mode, Scene *curscene)
 					SpaceText *st= (SpaceText *)sl;
 
 					st->text= restore_pointer_by_name(newmain, (ID *)st->text);
+					if(st->text==NULL) st->text= newmain->text.first;
 				}
 				else if(sl->spacetype==SPACE_SCRIPT) {
 					SpaceScript *sc= (SpaceScript *)sl;

source/blender/src/toets.c

@@ -950,8 +950,10 @@ int blenderqread(unsigned short event, short val)
 				return 0;
 			}
 			else if(G.qual==LR_ALTKEY) {
-				BIF_undo_menu();
-				return 0;
+				if(curarea->spacetype!=SPACE_TEXT) {
+					BIF_undo_menu();
+					return 0;
+				}
 			}
 		}
 		break;