If extra arguments after -get/-set matched one of the recognized
keywords ('icc', 'xmp', etc.), the parser would overwrite the
`config->args[]` allocation, as only one argument was expected.
The additional arguments are now treated as input files. This has the
side effect of allowing input files to be named the same as one of the
keywords.
Bug: webp:427503509
Change-Id: Ic48c94b75349109638e938781024be0a783ff267