busybox: fix ash segfaults after interrupting applet

Backported fix from Busybox v1.36.

DONE: RTOS-773

busybox/20-fix-ash-nofork-interrupted.patch

@@ -0,0 +1,23 @@
+diff --git a/shell/ash.c b/shell/ash.c
+--- a/shell/ash.c
++++ b/shell/ash.c
+@@ -9745,9 +9745,18 @@ evalcommand(union node *cmd, int flags)
+ 		/* find_command() encodes applet_no as (-2 - applet_no) */
+ 		int applet_no = (- cmdentry.u.index - 2);
+ 		if (applet_no >= 0 && APPLET_IS_NOFORK(applet_no)) {
++			INT_OFF;
+ 			listsetvar(varlist.list, VEXPORT|VSTACK);
+-			/* run <applet>_main() */
++			/*
++			 * Run <applet>_main().
++			 * Signals (^C) can't interrupt here.
++			 * Otherwise we can mangle stdio or malloc internal state.
++			 * This makes applets which can run for a long time
++			 * and/or wait for user input ineligible for NOFORK:
++			 * for example, "yes" or "rm" (rm -i waits for input).
++			 */
+ 			status = run_nofork_applet(applet_no, argv);
++			INT_ON;
+ 			break;
+ 		}
+ #endif