Add fuzzing stub for ReadFeeEstimates

src/fuzzing/ReadFeeEstimates/fuzz.cpp

@@ -0,0 +1,13 @@
+#include "txmempool.h"
+
+int main (int argc, char *argv[]) {
+    CFeeRate rate;
+    CTxMemPool mempool(rate);
+    CAutoFile est_filein(fopen(argv[1], "rb"), SER_DISK, CLIENT_VERSION);
+
+    if (mempool.ReadFeeEstimates(est_filein)) {
+        return 0;
+    } else {
+        return -1;
+    }
+}