Fix failure to honour OOM status in qemuParseNBDString

In qemuParseNBDString, if the virURIParse fails, the
error is not reported to the caller. Instead execution
falls through to the non-URI codepath causing memory
leaks later on.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/qemu/qemu_command.c

@@ -3556,9 +3556,9 @@ qemuParseNBDString(virDomainDiskDefPtr disk)
     virURIPtr uri = NULL;
 
     if (strstr(disk->src, "://")) {
-        uri = virURIParse(disk->src);
-        if (uri)
-            return qemuParseDriveURIString(disk, uri, "nbd");
+        if (!(uri = virURIParse(disk->src)))
+            return -1;
+        return qemuParseDriveURIString(disk, uri, "nbd");
     }
 
     if (VIR_ALLOC(h) < 0)