Multiple lib install command with the same local library results in duplicates in lib_deps

[valeros]

When installing a library from a local source (e.g. a zip archive) several times, PlatformIO duplicates this library in lib_deps each time although the library is already installed.

Steps to Reproduce

1. Download any library in a zip archive.
2. Run pio lib install /path/to/archive.zip multiple times.
3. See duplicated entries in the lib_deps section.

Actual Results

...
lib_deps = 
	E:\my_lib-master.zip
	E:\my_lib-master.zip
	E:\my_lib-master.zip
	E:\my_lib-master.zip
	E:\my_lib-master.zip
....

Expected Results

PlatformIO reports that the library is already installed.