Set float rounding mode on non-Windows platforms

Sys_SetFloatEnv in sys_unix.c existed but was not called. It sets the
rounding mode to "to nearest" which is the default on Linux. Might be
required on other platforms, I don't know.

code/sys/sys_unix.c

@@ -816,6 +816,8 @@ void Sys_PlatformInit( void )
 	signal( SIGIOT, Sys_SigHandler );
 	signal( SIGBUS, Sys_SigHandler );
 
+	Sys_SetFloatEnv();
+
 	stdinIsATTY = isatty( STDIN_FILENO ) &&
 		!( term && ( !strcmp( term, "raw" ) || !strcmp( term, "dumb" ) ) );
 }