term: send proper reset sequence when black background is forced

When using the force black background command-line option or configuration
option an invalid reset sequence is sent following a coloured output item 
in the CLI, the result is that the colour is not 'turned off' and continues
until the next non-default coloured text output.

A reset sequence is already defined in term.c, but the ast_term_reset
function doesn't use it, instead building it's own invalid sequence and 
returning that.

This patch changes that behaviour, removing the building of a reset sequence
and instead using the pre-built constant 'enddata' which is a suitable reset
sequence for this purpose.

ASTERISK-24896 #close
Reported by: Dan Tucny

Change-Id: I56323899123ae3264900389cae1f5b252aa3bf43

main/term.c

@@ -311,8 +311,7 @@ const char *ast_term_color(int fgcolor, int bgcolor)
 const char *ast_term_reset(void)
 {
 	if (ast_opt_force_black_background) {
-		static const char reset[] = { ESC, '[', COLOR_BLACK + 10, 'm', 0 };
+		return enddata;
-		return reset;
 	} else {
 		return quitdata;
 	}