log: Clarify that failure to read fee_estimates.dat is non-fatal

An uppercase "ERROR" in the log might indicate a fatal error. Though,
all read-failures for fee_estimates.dat are non-fatal, so avoid the
"ERROR".

Before:
ERROR: CBlockPolicyEstimator::Read(): up-version (149900) fee estimate file

After:
CBlockPolicyEstimator::Read(): unable to read policy estimator data (non-fatal): up-version (149900) fee estimate file

Author: MarcoFalke

src/policy/fees.cpp

@@ -909,8 +909,9 @@ bool CBlockPolicyEstimator::Read(CAutoFile& filein)
         LOCK(m_cs_fee_estimator);
         int nVersionRequired, nVersionThatWrote;
         filein >> nVersionRequired >> nVersionThatWrote;
-        if (nVersionRequired > CLIENT_VERSION)
-            return error("CBlockPolicyEstimator::Read(): up-version (%d) fee estimate file", nVersionRequired);
+        if (nVersionRequired > CLIENT_VERSION) {
+            throw std::runtime_error(strprintf("up-version (%d) fee estimate file", nVersionRequired));
+        }
 
         // Read fee estimates file into temporary variables so existing data
         // structures aren't corrupted if there is an exception.
@@ -928,8 +929,9 @@ bool CBlockPolicyEstimator::Read(CAutoFile& filein)
             std::vector<double> fileBuckets;
             filein >> fileBuckets;
             size_t numBuckets = fileBuckets.size();
-            if (numBuckets <= 1 || numBuckets > 1000)
+            if (numBuckets <= 1 || numBuckets > 1000) {
                 throw std::runtime_error("Corrupt estimates file. Must have between 2 and 1000 feerate buckets");
+            }
 
             std::unique_ptr<TxConfirmStats> fileFeeStats(new TxConfirmStats(buckets, bucketMap, MED_BLOCK_PERIODS, MED_DECAY, MED_SCALE));
             std::unique_ptr<TxConfirmStats> fileShortStats(new TxConfirmStats(buckets, bucketMap, SHORT_BLOCK_PERIODS, SHORT_DECAY, SHORT_SCALE));