driver: Fix condition for calling dumpReproducer

Previously, `dumpReproducer` was called for `@FuzzTest`s using Autofuzz,
which is implemented as a static fuzz target method.

Author: fmeum

src/main/java/com/code_intelligence/jazzer/driver/FuzzTargetRunner.java

@@ -316,7 +316,7 @@ private static int runOne(long dataPtr, int dataLength) {
     // that satisfies the same purpose.
     // It also doesn't support the experimental mutator yet as that requires implementing Java code
     // generation for mutators.
-    if (fuzzTargetInstance == null && !useExperimentalMutator) {
+    if (findingHandler == null && !useExperimentalMutator) {
       dumpReproducer(data);
     }