Avoid leaking file descriptors in RegisterLoad

This is pretty trivial, but if there's an error here we'll leak a file
descriptor. Changed it to always close the file.

src/dash-tx.cpp

@@ -149,13 +149,14 @@ static void RegisterLoad(const string& strInput)
         valStr.insert(valStr.size(), buf, bread);
     }
 
-    if (ferror(f)) {
+    int error = ferror(f);
+    fclose(f);
+
+    if (error) {
         string strErr = "Error reading file " + filename;
         throw runtime_error(strErr);
     }
 
-    fclose(f);
-
     // evaluate as JSON buffer register
     RegisterSetJson(key, valStr);
 }