virqemu: Reflect return type of virJSONValueArraySize()

The virJSONValueArraySize() function return ssize_t (with
possibly returning -1 if the passed json is not an array).
Storing the return value into size_t is possibly dangerous then.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/util/virqemu.c

@@ -85,7 +85,7 @@ virQEMUBuildCommandLineJSONArrayNumbered(const char *key,
                                          virBufferPtr buf)
 {
     const virJSONValue *member;
-    size_t nelems = virJSONValueArraySize(array);
+    ssize_t nelems = virJSONValueArraySize(array);
     char *prefix = NULL;
     size_t i;
     int ret = 0;