linux/Battery.c: make sure fd is always closed

Detected by Coverity:
https://scan8.coverity.com/reports.htm#v13252/p10402/fileInstanceId=22093957&defectInstanceId=7543348&mergedDefectId=174180

linux/Battery.c

@@ -110,16 +110,13 @@ static ACPresence procAcpiCheck() {
       char statePath[50];
       xSnprintf((char *) statePath, sizeof statePath, "%s/%s/state", power_supplyPath, entryName);
       FILE* file = fopen(statePath, "r");
-
       if (!file) {
          isOn = AC_ERROR;
          continue;
       }
-
       char* line = String_readLine(file);
-      if (!line) continue;
-
       fclose(file);
+      if (!line) continue;
 
       const char *isOnline = String_getToken(line, 2);
       free(line);