Fixed error: Would crash often if only one foreground color.

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required (VERSION 3.2)
 project(identiconpp
-        VERSION 0.3.3
+        VERSION 0.3.4
         LANGUAGES CXX
 )
 

src/identiconpp.cpp

@@ -133,7 +133,7 @@ Magick::Color Identiconpp::get_color(const uint16_t firstbit,
     // a power of 2.
     if (bits > (_foreground.size() - 1))
     {
-        bits -= (_foreground.size() - 1);
+        bits -= _foreground.size();
     }
 
     // Lookup und set color