patch 8.0.1096: terminal window in Normal mode has wrong background

Problem:    Terminal window in Normal mode has wrong background.
Solution:   Store the default background and use it for clearning until the
            end of the line.  Not for below the last line, since there is no
            text there.
diff --git a/src/screen.c b/src/screen.c
index e0d4af8..40c9a15 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -3139,6 +3139,7 @@
 #endif
 #ifdef FEAT_TERMINAL
     int		get_term_attr = FALSE;
+    int		term_attr = 0;		/* background for terminal window */
 #endif
 
     /* draw_state: items that are drawn in sequence: */
@@ -3256,6 +3257,7 @@
     {
 	extra_check = TRUE;
 	get_term_attr = TRUE;
+	term_attr = term_get_attr(wp->w_buffer, 0, 0);
     }
 #endif
 
@@ -5057,6 +5059,9 @@
 # ifdef FEAT_DIFF
 			    diff_hlf != (hlf_T)0 ||
 # endif
+# ifdef FEAT_TERMINAL
+			    term_attr != 0 ||
+# endif
 			    line_attr != 0
 			) && (
 # ifdef FEAT_RIGHTLEFT
@@ -5091,6 +5096,15 @@
 			}
 		    }
 # endif
+# ifdef FEAT_TERMINAL
+		    if (term_attr != 0)
+		    {
+			char_attr = term_attr;
+			if (wp->w_p_cul && lnum == wp->w_cursor.lnum)
+			    char_attr = hl_combine_attr(char_attr,
+							    HL_ATTR(HLF_CUL));
+		    }
+# endif
 		}
 #endif
 	    }