fixdep: avoid underflow when end of entry doesn't coincide with EOF

Bug: https://bugs.gentoo.org/893776
Closes: https://bugs.busybox.net/show_bug.cgi?id=15326
Signed-off-by: Arsen Arsenović <arsen@gentoo.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

scripts/basic/fixdep.c

@@ -338,6 +338,11 @@ void parse_dep_file(void *map, size_t len)
 			do p--; while (!isalnum((unsigned char)*p));
 			p++;
 		}
+		if (p < m) {
+			/* we've consumed the last filename of this list
+			   already.  */
+			break;
+		}
 		memcpy(s, m, p-m); s[p-m] = 0;
 		if (strrcmp(s, "include/autoconf.h") &&
 		    strrcmp(s, "arch/um/include/uml-config.h") &&