fix: better compatibility under busybox, silence buggy unzlma versions (fix #432)

src/libs/300_kernel_extract.sh

@@ -88,7 +88,9 @@ try_decompress() {
         fi
         pos=${pos%%:*}
         # shellcheck disable=SC2086
-        tail -c+$pos "$6" 2>/dev/null | $3 $4 >"$g_kerneltmp" 2>/dev/null
+        # wrap in subshell so that if $3 segfaults (e.g. old BusyBox unlzma on random data),
+        # the "Segmentation fault" message printed by the shell goes to /dev/null
+        (tail -c+$pos "$6" 2>/dev/null | $3 $4 >"$g_kerneltmp" 2>/dev/null) 2>/dev/null
         ret=$?
         if [ ! -s "$g_kerneltmp" ]; then
             # don't rely on $ret, sometimes it's != 0 but worked