devtools, utxo-snapshot: Fix block height out of range

Handle the Block height out of range error gracefully by checking if
the node has synchronized to or beyond the required block height,
otherwise without this validation the node would keep the network
disabled if the user selected that option.

Provide a user-friendly message if the block height is out of range
and exit the script cleanly.

Author: pablomartin4btc

contrib/devtools/utxo_snapshot.sh

@@ -36,6 +36,16 @@ if (( GENERATE_AT_HEIGHT < PRUNED )); then
   exit 1
 fi
 
+# Check current block height to ensure the node has synchronized past the required block
+CURRENT_BLOCK_HEIGHT=$(${BITCOIN_CLI_CALL} getblockcount)
+PIVOT_BLOCK_HEIGHT=$(( GENERATE_AT_HEIGHT + 1 ))
+
+if (( PIVOT_BLOCK_HEIGHT > CURRENT_BLOCK_HEIGHT )); then
+  (>&2 echo "Error: The node has not yet synchronized to block height ${PIVOT_BLOCK_HEIGHT}.")
+  (>&2 echo "Please wait until the node has synchronized past this block height and try again.")
+  exit 1
+fi
+
 # Early exit if file at OUTPUT_PATH already exists
 if [[ -e "$OUTPUT_PATH" ]]; then
   (>&2 echo "Error: $OUTPUT_PATH already exists or is not a valid path.")