Fix using patterns stored as table/set indices

Pattern values used as table/set indices are stored in serialized form
using just the pattern text, but re-creating the value from that didn't
fully initialize/compile the regex matcher after (re-)creating it from
that pattern text.

src/CompHash.cc

@@ -891,6 +891,11 @@ const char* CompositeHash::RecoverOneVal(const HashKey* k, const char* kp0,
 				re = new RE_Matcher(kp1, kp1 + len[0]);
 				kp1 += len[0] + len[1];
 				}
+
+			if ( ! re->Compile() )
+				reporter->InternalError("failed compiling table/set key pattern: %s",
+				                        re->PatternText());
+
 			*pval = make_intrusive<PatternVal>(re);
 			}
 			break;