Check shadowsSpawnLimit() before building RRLs for negotiator. #6749
Check shadowsSpawnLimit() before building RRLs for negotiator. #6749

Before, shadowsSpawnLimit() was checked after building the RRLs, but
before sending them to the negotiator. The building of the RRLs is a
waste of time if it returns 0. This checks both the CURB_MATCHMAKING
expreession and the schedd's limits on number of shadows.

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