Issue #50 Interaction between -0 and demand for a sold item

Try to honor -0 a little more while trying to avoid the risk of users making items inaccessible.

This change means that -0 will be honored if the "fromStn" price is 0, but if the station is
buying an item (fromStn > 0) then it will revert to using the default (unk) for the demand
field.

README.txt

@@ -26,6 +26,7 @@ files from other commanders to fill out your database.
 v5.0.1 In Progress
 . (kfsone) Issue #49 Errors in Ambiguity Error
 . (kfsone) Issue #51 L and ? items weren't honoring qty limits
+. (kfsone) Issue #50 Interaction between -0 and demand for a sold item
 
 v5.0.0 Oct 31/2014
 . (kfsone) Initial Beta 3 changes

prices.py

@@ -139,6 +139,11 @@ def itemQtyAndLevel(quantity, level):
         file.write("  {}".format("Timestamp"))
     file.write("\n\n")
 
+
+    naIQL = itemQtyAndLevel(0, 0)
+    unkIQL = itemQtyAndLevel(-2, -2)
+    defIQL = itemQtyAndLevel(-1, -1)
+
     for (sysID, stnID, catID, itemID, fromStn, toStn, modified, demand, demandLevel, stock, stockLevel) in cur:
         system = systems[sysID]
         if system is not lastSys:
@@ -162,11 +167,16 @@ def itemQtyAndLevel(quantity, level):
         if withSupply:
             # Is this item on sale?
             if toStn > 0:
-                demandStr = itemQtyAndLevel(-2, -2)
+                # Zero demand-price gets default demand, which will
+                # be either unknown or zero depending on -0.
+                # If there is a price, always default to unknown
+                # because it can be sold here but the demand is just
+                # not useful as data.
+                demandStr = defIQL if fromStn <= 0 else unkIQL
                 stockStr  = itemQtyAndLevel(stock, stockLevel)
             else:
                 demandStr = itemQtyAndLevel(demand, demandLevel)
-                stockStr = itemQtyAndLevel(0, 0)
+                stockStr = naIQL
             file.write("  {:>{lvlwidth}} {:>{lvlwidth}}".format(
                         demandStr,
                         stockStr,