syz-fuzzer: fix nil deref in deserializeInput

We build choice table only after we received the initial corpus,
so we don't check the initial corpus in deserializeInput,
we check it later in BuildChoiceTable.

syz-fuzzer/fuzzer.go

@@ -457,7 +457,11 @@ func (fuzzer *Fuzzer) deserializeInput(inp []byte) *prog.Prog {
 	if err != nil {
 		log.Fatalf("failed to deserialize prog: %v\n%s", err, inp)
 	}
-	fuzzer.checkDisabledCalls(p)
+	// We build choice table only after we received the initial corpus,
+	// so we don't check the initial corpus here, we check it later in BuildChoiceTable.
+	if fuzzer.choiceTable != nil {
+		fuzzer.checkDisabledCalls(p)
+	}
 	if len(p.Calls) > prog.MaxCalls {
 		return nil
 	}