Fix a crash when going into recovery mode.

When going into recovery mode withoug recovery command file present, uncrypt crashes
and the device gets stuck and eventually shuts down.

Check that the command file is present before trying to read from it.

Change-Id: If0192d597032be0067738e437188d92993ce56f7
diff --git a/uncrypt/uncrypt.c b/uncrypt/uncrypt.c
index 1f0f59d..7c2d994 100644
--- a/uncrypt/uncrypt.c
+++ b/uncrypt/uncrypt.c
@@ -149,9 +149,14 @@
     int count = 0;
     char temp[1024];
 
-    FILE* fo = fopen(RECOVERY_COMMAND_FILE_TMP, "w");
+
 
     FILE* f = fopen(RECOVERY_COMMAND_FILE, "r");
+    if (f == NULL) {
+        return NULL;
+    }
+    FILE* fo = fopen(RECOVERY_COMMAND_FILE_TMP, "w");
+
     while (fgets(temp, sizeof(temp), f)) {
         printf("read: %s", temp);
         if (strncmp(temp, "--update_package=", strlen("--update_package=")) == 0) {