sslCa should be set NULL after parseConfigLine in SSLCertLookup.cc

If previous configs in ssl_multicert.config have ssl_ca_name set, but the following lines do NOT set it, traffic.out will report:
Server

ERROR: SSL ERROR: Cannot use server certificate chain file: <proxy.config.ssl.client.CA.cert.path>

Patches:
— iocore/net/SSLCertLookup.cc.orig 2012-09-24 16:21:57.000000000 +0800
+++ iocore/net/SSLCertLookup.cc 2012-09-24 16:43:05.000000000 +0800
@@ -249,6 +249,7 @@ SSLCertLookup::buildTable()
ats_free(addr);
addr = NULL;
sslCert = NULL;
+ sslCa = NULL;
priKey = NULL;
}
} // else