Fix fail over to vfat from exfat

Fix issues with MD5 checking using chdir and leaving the working
dir in a subfolder that prevented unmounting sometimes.

Change-Id: I01a563d722f474297ed3f7a30064c3a61748ade3
diff --git a/twrp-functions.cpp b/twrp-functions.cpp
index 0c4471a..4a5dec2 100644
--- a/twrp-functions.cpp
+++ b/twrp-functions.cpp
@@ -62,8 +62,7 @@
 	if (Path_Exists(MD5_File)) {
 		DirPath = Get_Path(File);
 		MD5_File = Get_Filename(MD5_File);
-		chdir(DirPath.c_str());
-		Command = "/sbin/busybox md5sum -c " + MD5_File;
+		Command = "cd '" + DirPath + "' && /sbin/busybox md5sum -c '" + MD5_File + "'";
 		Exec_Cmd(Command, result);
 		pos = result.find(":");
 		if (pos != string::npos) {