pow() doesn't work for negative values

[Dimitar Misev]

As reported on the mailing list:

in expression > pow(x, 0.756), if x evaluates to 0 or greater, everything works, but if evaluates to negative value, an error 400 is thrown. The rasserver log displays only this:
Error number: 510 Token: POW Line: 1 Column: 15

A quick test to reproduce:

$ directql -q 'select csv(pow(<[0:0] -5f>, 0.765))' --out string -d /d/rasdata/RASBASE 
directql: rasdaman query tool v1.0, rasdaman v9.4.0-beta2.
opening database /d/rasdata/RASBASE at localhost:7001... [INFO] - Connected successfully to '/d/rasdata/RASBASE'
 [INFO] - initialized blob file storage handler with root data directory /d/rasdata/TILES/
 ok
Executing retrieval query... [INFO] - Request: 'select csv(pow(<[0:0] -5f>, 0.765))'...
 [INFO] - parsing...
 [INFO] - checking semantics...
 [INFO] - evaluating...
[FATAL] - QtUnaryInduce::computeUnaryMDDOp caught errno error (510) in unaryinduce
Getting result...ok.
directql done.