Fix an issue where demolishing a building would result in a negative amount of power.

src/power.c

@@ -181,7 +181,7 @@ void usePower(int player, float quantity)
 void addPower(int player, float quantity)
 {
 	ASSERT(player < MAX_PLAYERS, "addPower: Bad player (%u)", player);
-
+	ASSERT(asPower[player].currentPower + quantity >= 0, "not enough power");
 	asPower[player].currentPower += quantity;
 }
 
@@ -233,6 +233,7 @@ float updateExtractedPower(STRUCTURE	*psBuilding)
 		pResExtractor->timeLastUpdated = gameTime;
 		extractedPoints += pointsToAdd;
 	}
+	ASSERT(extractedPoints > 0, "extracted negative amount of power");
 	return extractedPoints;
 }
 
@@ -297,6 +298,7 @@ void updateCurrentPower(POWER_GEN *psPowerGen, UDWORD player)
 	}
 
 	asPower[player].currentPower += (extractedPower * psPowerGen->multiplier) / 100;
+	ASSERT(asPower[player].currentPower >= 0, "negative power");
 }
 
 // only used in multiplayer games.
@@ -305,6 +307,7 @@ void setPower(int player, float power)
 	ASSERT(player < MAX_PLAYERS, "setPower: Bad player (%u)", player);
 
 	asPower[player].currentPower = power;
+	ASSERT(asPower[player].currentPower >= 0, "negative power");
 }
 
 float getPower(int player)

src/structure.c

@@ -1156,8 +1156,8 @@ void structureBuild(STRUCTURE *psStruct, DROID *psDroid, int buildPoints)
 	}
 	else
 	{
-		// get half the power back for repairing 
-		powerNeeded = ((psStruct->currentBuildPts + buildPoints) * structureTotalReturn(psStruct))/(psStruct->pStructureType->buildPoints) -
+		// get half the power back for demolishing 
+		powerNeeded = (((int)psStruct->currentBuildPts + buildPoints) * structureTotalReturn(psStruct))/(psStruct->pStructureType->buildPoints) -
 		               (psStruct->currentBuildPts * structureTotalReturn(psStruct))/(psStruct->pStructureType->buildPoints);
 		buildPointsToAdd = buildPoints;
 		addPower(psDroid->player, -powerNeeded);