- Updated the item price/sell reading code to enable 'null' values. The difference between a blank value and 0 is that when the value is blank, it should automatically take half/double the other value. The previous behaviour did this automatically and didn't let you specify, for example, if you wanted a given item to sell for 0.
- Also added a warning when an item in the db has an exploitable price (through overcharge/discount).
git-svn-id: https://svn.code.sf.net/p/rathena/svn/trunk@11482 54d463be-8e91-2dee-dedb-b68131a5f0ec
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