Fix FD leak when checking lock dir permissions.

`mkstemp(3)` creates and opens a file descriptor for a temporary file,
but this file descriptor was immediately discarded in favour of
`fopen(3)`'ing the file by name and using that `FILE *` stream. I'm sure
whoever originally wrote this code meant to use `mktemp(3)` instead,
which only creates a unique file from a template name (equivalent to
`mktemp(1)`).

Author: MrDOS

src/main/c/src/SerialImp.c

@@ -5835,7 +5835,7 @@ int check_group_uucp()
 	strcat(testLockAbsFileName, testLockFileDirName);
 	strcat(testLockAbsFileName, "/");
 	strcat(testLockAbsFileName, testLockFileName);
-	if ( 0 == mkstemp(testLockAbsFileName) )
+	if ( NULL == mktemp(testLockAbsFileName) )
 	{
 		free(testLockAbsFileName);
 		report_error("check_group_uucp(): mktemp malformed string - \