Only write bram data to ASCII output if bram data is present, fixes #228

Signed-off-by: Clifford Wolf <clifford@clifford.at>

icepack/icepack.cc

diff --git a/icepack/icepack.cc b/icepack/icepack.cc
index 5b1745a..d441042 100644
--- a/icepack/icepack.cc
+++ b/icepack/icepack.cc
@@ -912,7 +912,7 @@
 			ofs << '\n';
 		}
 
-		if (cic.tile_type == "ramb")
+		if (cic.tile_type == "ramb" && !this->bram.empty())
 		{
 			BramIndexConverter bic(this, x, y);
 			ofs << stringf(".ram_data %d %d\n", x, y);