qemu: check if block I/O limits fit into long long

We can only pass values up to LLONG_MAX through JSON
and QEMU checks if the int64_t number is not negative
at startup since 1.5.0.

https://bugzilla.redhat.com/show_bug.cgi?id=974010

src/qemu/qemu_driver.c

@@ -14099,6 +14099,13 @@ qemuDomainSetBlockIoTune(virDomainPtr dom,
     for (i = 0; i < nparams; i++) {
         virTypedParameterPtr param = &params[i];
 
+        if (param->value.ul > LLONG_MAX) {
+            virReportError(VIR_ERR_OVERFLOW,
+                           _("block I/O throttle limit value must"
+                             " be less than %llu"), LLONG_MAX);
+            goto endjob;
+        }
+
         if (STREQ(param->field, VIR_DOMAIN_BLOCK_IOTUNE_TOTAL_BYTES_SEC)) {
             info.total_bytes_sec = param->value.ul;
             set_bytes = true;