MINOR: mux-quic: close on qcs allocation failure

MINOR: mux-quic: close on qcs allocation failure

Emit a CONNECTION_CLOSE with INTERNAL_ERROR code each time qcs
allocation fails. This can happen in two cases :
* when creating a local stream through application layer
* when instantiating a remote stream through qcc_get_qcs()

In both cases, error paths are already in place to interrupt the current
operation and a CONNECTION_CLOSE will be emitted soon after.

This should be backported up to 2.7.