Do not allow the manual insertion of a directory (without filename) into the import dialog and thus prevent an assertion.

Fixes: #7437(cherry picked from commit afd897029917a083fbeb84cccd4e6cb0a21db7ed)

src/frontends/qt4/GuiView.cpp

@@ -2119,6 +2119,18 @@ void GuiView::importDocument(string const & argument)
 	// get absolute path of file
 	FileName const fullname(support::makeAbsPath(filename));
 
+	// Can happen if the user entered a path into the dialog
+	// (see bug #7437)
+	if (fullname.onlyFileName().empty()) {
+		docstring msg = bformat(_("The file name '%1$s' is invalid!\n"
+					  "Aborting import."),
+					from_utf8(fullname.absFileName()));
+		frontend::Alert::error(_("File name error"), msg);
+		message(_("Canceled."));
+		return;
+	}
+
+
 	FileName const lyxfile(support::changeExtension(fullname.absFileName(), ".lyx"));
 
 	// Check if the document already is open

status.21x

@@ -65,6 +65,8 @@ What's new
 
 - Fix crash when CheckTeX hits mathed (bug 8798).
 
+- Fix assertion when entering a path into the import dialog (bug 7437).
+
 - Failed instant preview compilation now returns an error. And a red box is 
   drawn around very small preview imagines, so they can be seen (bug 7522).