[core] fix abort in http-parseopts (fixes #2945)

fix abort in server.http-parseopts with url-path-2f-decode enabled

(thx stze)

x-ref:
  "Security - SIGABRT during GET request handling with url-path-2f-decode enabled"
  https://redmine.lighttpd.net/issues/2945

src/burl.c

@@ -252,8 +252,10 @@ static int burl_normalize_2F_to_slash_fix (buffer *b, int qs, int i)
         }
     }
     if (qs >= 0) {
-        memmove(s+j, s+qs, blen - qs);
-        j += blen - qs;
+        const int qslen = blen - qs;
+        memmove(s+j, s+qs, (size_t)qslen);
+        qs = j;
+        j += qslen;
     }
     buffer_string_set_length(b, j);
     return qs;

src/t/test_burl.c

@@ -97,6 +97,8 @@ static void test_burl_normalize (void) {
     flags |= HTTP_PARSEOPT_URL_NORMALIZE_PATH_2F_DECODE;
     run_burl_normalize(psrc, ptmp, flags, __LINE__, CONST_STR_LEN("/a/b?c=/"), CONST_STR_LEN("/a/b?c=/"));
     run_burl_normalize(psrc, ptmp, flags, __LINE__, CONST_STR_LEN("/a/b?c=%2f"), CONST_STR_LEN("/a/b?c=/"));
+    run_burl_normalize(psrc, ptmp, flags, __LINE__, CONST_STR_LEN("%2f?"), CONST_STR_LEN("/?"));
+    run_burl_normalize(psrc, ptmp, flags, __LINE__, CONST_STR_LEN("/%2f?"), CONST_STR_LEN("//?"));
     run_burl_normalize(psrc, ptmp, flags, __LINE__, CONST_STR_LEN("/a%2fb"), CONST_STR_LEN("/a/b"));
     run_burl_normalize(psrc, ptmp, flags, __LINE__, CONST_STR_LEN("/a%2Fb"), CONST_STR_LEN("/a/b"));
     run_burl_normalize(psrc, ptmp, flags, __LINE__, CONST_STR_LEN("/a%2fb?c=/"), CONST_STR_LEN("/a/b?c=/"));