patch 8.1.1819: :pedit does not work with a popup preview window

Problem:    :pedit does not work with a popup preview window.
Solution:   Avoid aborting with an error. (fixes #4777)  Also double check
            that after prepare_tagpreview() the current window is not a
            popup window.
diff --git a/src/search.c b/src/search.c
index 626bc3d..88b6c09 100644
--- a/src/search.c
+++ b/src/search.c
@@ -5632,6 +5632,11 @@
 		    redraw_later(VALID);
 		    win_enter(curwin_save, TRUE);
 		}
+# ifdef FEAT_TEXT_PROP
+		else if (WIN_IS_POPUP(curwin))
+		    // can't keep focus in popup window
+		    win_enter(firstwin, TRUE);
+# endif
 #endif
 		break;
 	    }