Reset FirstFreeEntry in ACSStringPool::ReadStrings()

- Fixed: When an ACS string pool was read from a savegame, FirstFreeEntry
  would not be updatedt, except by the Clear() function. This left FirstFreeEntry
  at 0, which meant the next string added to the pool would always go in
  slot 0, whether it was free or not.

src/p_acs.cpp

@@ -575,11 +575,7 @@ int ACSStringPool::InsertString(FString &str, unsigned int h, unsigned int bucke
 	}
 	else
 	{ // Scan for the next free entry
-		unsigned int i;
-		for (i = FirstFreeEntry + 1; i < Pool.Size() && Pool[i].Next != FREE_ENTRY; ++i)
-		{
-		}
-		FirstFreeEntry = i;
+		FindFirstFreeEntry(FirstFreeEntry + 1);
 	}
 	PoolEntry *entry = &Pool[index];
 	entry->Str = str;
@@ -590,6 +586,23 @@ int ACSStringPool::InsertString(FString &str, unsigned int h, unsigned int bucke
 	return index | STRPOOL_LIBRARYID_OR;
 }
 
+//============================================================================
+//
+// ACSStringPool :: FindFirstFreeEntry
+//
+// Finds the first free entry, starting at base.
+//
+//============================================================================
+
+void ACSStringPool::FindFirstFreeEntry(unsigned base)
+{
+	while (base < Pool.Size() && Pool[base].Next != FREE_ENTRY)
+	{
+		base++;
+	}
+	FirstFreeEntry = base;
+}
+
 //============================================================================
 //
 // ACSStringPool :: ReadStrings
@@ -638,6 +651,7 @@ void ACSStringPool::ReadStrings(PNGHandle *png, DWORD id)
 		{
 			delete[] str;
 		}
+		FindFirstFreeEntry(0);
 	}
 }
 
@@ -690,6 +704,7 @@ void ACSStringPool::Dump() const
 			Printf("%4u. (%2d) \"%s\"\n", i, Pool[i].LockCount, Pool[i].Str.GetChars());
 		}
 	}
+	Printf("First free %u\n", FirstFreeEntry);
 }
 
 //============================================================================

src/p_acs.h

@@ -100,6 +100,7 @@ public:
 private:
 	int FindString(const char *str, size_t len, unsigned int h, unsigned int bucketnum);
 	int InsertString(FString &str, unsigned int h, unsigned int bucketnum, const SDWORD *stack, int stackdepth);
+	void FindFirstFreeEntry(unsigned int base);
 
 	enum { NUM_BUCKETS = 251 };
 	enum { FREE_ENTRY = 0xFFFFFFFE };	// Stored in PoolEntry's Next field