Check the fd handle before attempting to use it in GNSS HAL

Bug: 171851344
Test: run vts -a x86 -m vts_ibase_test -t VtsHalBaseV1_0TargetTest#Debug
Change-Id: Ieee0977812fe6a9a9ca4bb2fe9ab61899b4d0df5
diff --git a/gnss/common/utils/default/include/v2_1/GnssTemplate.h b/gnss/common/utils/default/include/v2_1/GnssTemplate.h
index 7c3c58a..cbf3933 100644
--- a/gnss/common/utils/default/include/v2_1/GnssTemplate.h
+++ b/gnss/common/utils/default/include/v2_1/GnssTemplate.h
@@ -689,6 +689,10 @@
 template <class T_IGnss>
 Return<void> GnssTemplate<T_IGnss>::debug(const hidl_handle& fd,
                                           const hidl_vec<hidl_string>& options) {
+    if (fd == nullptr || fd->numFds == 0) {
+        return Void();
+    }
+
     if (options.size() == 0) {
         return help(fd);
     } else if (options[0] == "location") {