patch 8.2.0791: a second popup window with terminal causes trouble

Problem:    A second popup window with terminal causes trouble.
Solution:   Disallow opening a second terminal-popup window. (closes #6101,
            closes #6103) Avoid defaulting to an invalid line number.
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 94a3367..5447b74 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -2918,8 +2918,12 @@
 	{
 	    case ADDR_LINES:
 	    case ADDR_OTHER:
-		// default is current line number
-		eap->line2 = curwin->w_cursor.lnum;
+		// Default is the cursor line number.  Avoid using an invalid
+		// line number though.
+		if (curwin->w_cursor.lnum > curbuf->b_ml.ml_line_count)
+		    eap->line2 = curbuf->b_ml.ml_line_count;
+		else
+		    eap->line2 = curwin->w_cursor.lnum;
 		break;
 	    case ADDR_WINDOWS:
 		eap->line2 = CURRENT_WIN_NR;