Fix crash with bad `parts[next]` index

nel/src/gui/css_style.cpp

@@ -1039,6 +1039,8 @@ namespace NLGUI
 						// second loop -> false && break
 						loop = !loop;
 
+						if (next < parts.size())
+						{
 							val = toLowerAscii(parts[next]);
 							if (val == "center")
 							{
@@ -1071,6 +1073,7 @@ namespace NLGUI
 									next++;
 								}
 							}
+						}
 					} while (loop);
 
 					//