nemo-places-sidebar.c: Don't show shadowed mounts, or mounts without

volumes.

ref:
linuxmint/cinnamon@af72ce0426515740e0

nemo-places-sidebar.c: Don't show shadowed mounts, or mounts without

volumes.

ref:
linuxmint/cinnamon@af72ce0426515740e0

file operations: Fix some memory leaks.

Spotted by valgrind.