enable save_kmz for wrapped ifg by fixing plot.scale_data2disp_unit()

[tshreve]

Description of proposed changes

Added changes to plot.py to not calculate WAVELENGTH when displaying a wrapped interferograms in radians. Previously, an error was thrown when running save_kmz.py, since there is no wavelength defined in isce2 wrapped interferogram metadata.

Reminders

• Fixes save_kmz.py for wrapped ISCE2 interferogram #1266
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• Pass Circle CI test (green)
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[yunjunz]

LGTM. Thank you @tshreve!

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