MSCW-reader reads in trends of all available year rather than only years selected with periods

[heikoklein]

Describe the bug

• Pyaerocom version: latest
• Configuration file (if applicable):
  • cfg_emep-status_trends.py.gz
• Error message (if applicable): On a 2 year = 24 timestep monthly evaluation, 48 timesteps (= all in subfolders) are read

Extracting timeseries data from large array (shape: (48, 520, 1200)). This may take a while...

To Reproduce Steps to reproduce the behavior:

1. create a trend-analysis with mscw-reader. Select periods to be smaller than available trend-years.
2. The mscw-reader will try to read/collocate all available trend-years, not only the necessary once.
3. pyaerocom takes much longer to evaluation (typically, only every 5th year are selected) and crashes due to timeouts.

Expected behavior The mscw-reader only reads years selected by periods.