Add missing header.

include/assimp/BaseImporter.h

@@ -53,6 +53,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include <assimp/types.h>
 #include <assimp/ProgressHandler.hpp>
+#include <exception>
 #include <set>
 #include <vector>
 #include <memory>