1,​8-​Naphthyridine-​3-​carboxylic acid, 7-​(3-​amino-​1-​pyrrolidinyl)​-​1-​(2,​4-​difluorophenyl)​-​6-​fluoro-​1,​4-​dihydro-​4-​oxo-​, hydrochloride (1:1)