Picture Viewer : incorrectly appends file extension

reactos-bootcd-0.4.15-dev-6725-ge685b25-x86-gcc-lin-dbg

• Open a Bmp
• Save as GIF
• Use "test" as file name
• File "test" is created while "test.gif" would be expected
• Win2K3 : Extension is added automatically

Likely to be fixed similarly to https://github.com/reactos/reactos/pull/5356 from katayama_hirofumi_mz for Paint