patch 8.0.1540: popup menu positioning fails with longer string

Problem:    Popup menu positioning fails with longer string.
Solution:   Only align with right side of window when width is less than
            'pumwidth' (closes #2661)
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index b0024e6..499b08b 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -772,6 +772,15 @@
   call term_sendkeys(buf, "GA\<C-N>")
   call VerifyScreenDump(buf, 'Test_popup_position_03', {'rows': 8})
 
+  " completed text wider than the window and 'pumwidth' smaller than available
+  " space
+  call term_sendkeys(buf, "\<Esc>u")
+  call term_sendkeys(buf, ":set pumwidth=20\<CR>")
+  call term_sendkeys(buf, "ggI123456789_\<Esc>")
+  call term_sendkeys(buf, "jI123456789_\<Esc>")
+  call term_sendkeys(buf, "GA\<C-N>")
+  call VerifyScreenDump(buf, 'Test_popup_position_04', {'rows': 10})
+  
   call term_sendkeys(buf, "\<Esc>u")
   call StopVimInTerminal(buf)
   call delete('Xtest')