patch 8.2.4775: SpellBad highlighting does not work in Konsole

Problem:    SpellBad highlighting does not work in Konsole.
Solution:   Do not keep t_8u defined for Konsole.  Redraw when t_8u is reset.
            (closes #10177)
diff --git a/src/term.c b/src/term.c
index 73c76cd..0aafebb 100644
--- a/src/term.c
+++ b/src/term.c
@@ -4775,9 +4775,10 @@
 	    // vandyke SecureCRT sends 1;136;0
 	}
 
-	// Konsole sends 0;115;0
-	else if (version == 115 && arg[0] == 0 && arg[2] == 0)
-	    term_props[TPR_UNDERLINE_RGB].tpr_status = TPR_YES;
+	// Konsole sends 0;115;0 - but t_u8 does not actually work, therefore
+	// commented out.
+	// else if (version == 115 && arg[0] == 0 && arg[2] == 0)
+	//     term_props[TPR_UNDERLINE_RGB].tpr_status = TPR_YES;
 
 	// GNU screen sends 83;30600;0, 83;40500;0, etc.
 	// 30600/40500 is a version number of GNU screen. DA2 support is added
@@ -4806,9 +4807,15 @@
 
 	// Unless the underline RGB color is expected to work, disable "t_8u".
 	// It does not work for the real Xterm, it resets the background color.
+	// This may cause some flicker.  Alternative would be to set "t_8u"
+	// here if the terminal is expected to support it, but that might
+	// conflict with what was set in the .vimrc.
 	if (term_props[TPR_UNDERLINE_RGB].tpr_status != TPR_YES && *T_8U != NUL)
+	{
 	    set_string_option_direct((char_u *)"t_8u", -1, (char_u *)"",
 								  OPT_FREE, 0);
+	    redraw_later(CLEAR);
+	}
 
 	// Only set 'ttymouse' automatically if it was not set
 	// by the user already.