Print warning about insufficient units only if target_units is a number

[hanase]

In our case, self.target_units is a dictionary that contains the required number of units for each building type. The selection itself is handled by our own custom_selection_func. Because the self.target_units is not a number, the warning about insufficient units is always printed, regardless of the actual numbers.

Here I added a condition that the warning should be printed only if self.target_units is a number. Other possibility is to print the warning only if custom_selection_func is not set.

[coveralls]

Pull Request Test Coverage Report for Build 35

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 95.737%

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Totals
Change from base Build 34:	0.005%
Covered Lines:	786
Relevant Lines:	821

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💛 - Coveralls

[janowicz]

Thanks for this @hanase! Looks good.