Make sure icon is json (ethereum-lists#2245)

One slipped as seen in ethereum-lists#2243

MUST be merged after ethereum-lists#2243

Author: ligi

processor/src/main/kotlin/org/ethereum/lists/chains/Main.kt

@@ -82,7 +82,12 @@ private fun createOutputFiles() {
         .forEach { iconLocation ->
 
             val jsonData = Klaxon().parseJsonArray(iconLocation.reader())
-            val iconName = iconLocation.toString().replace("../_data/icons/", "").replace(".json", "")
+
+            if (iconLocation.extension != "json") {
+                error("Icon must be json " + iconLocation)
+            }
+
+            val iconName = iconLocation.toString().removePrefix("../_data/icons/").removeSuffix(".json")
 
             val iconJson = JsonObject()
             iconJson["name"] = iconName