Fixed a minor bug in handling of automated xacts

There was a if statement with an inverse boolean meaning, which caused
some automated transaction postings to have a null amount.

src/xact.cc

@@ -367,7 +367,7 @@ void auto_xact_t::extend_xact(xact_base_t& xact, bool post_handler)
 	amount_t amt;
 	assert(post->amount);
 	if (! post->amount.commodity()) {
-	  if (! post_handler)
+	  if (post_handler)
 	    continue;
 	  assert(initial_post->amount);
 	  amt = initial_post->amount * post->amount;

test/baseline/opt-actual.test

@@ -2,6 +2,7 @@ print --actual
 <<<
 = account =~ /Books/
     Expenses:Taxes            0.05
+    Assets:Checking          -0.05
 
 2008/01/01 January
     Expenses:Books          $10.00