Same filename for input and output doesn't work

[robryk]

Split away form #19. We should probably open the output file for writing first and truncate it only after we have the output JPEG ready.

[khavishbhundoo]

ignore or delete that commit....sorry i am new to github

[khavishbhundoo]

I just started learning c++ so forgive my ignorance

Check my attempt to solve the problem
khavishbhundoo@f4c3a33

However i seems to get an issue in trying to get bazel to see my changes while compiling(sounds crazy and stupid)

I tried the following

Modified the error message (Guetzli processing failed) to something else and then ran bazel clean and bazel build -c opt //:guetzli.Surprising the error shown is still Guetzli processing failed

[Furniel]

I think we should allow optimization only with one image as argument, code will look like this:
https://github.com/Furniel/guetzli/commit/5252181fa2e1d79527b4618d7569b6e07477f0e1
With this patch image optimization works with input image or with input and optput images(output can be same).
That`s not final code, if we want allow use guetzli only with one arg we should check input image format. Everything works good if input image is jpg but if input is png - output will be written to png too now(that's not good idea).

[robryk]

@Furniel I don't want to encourage people to use the same file for input and output, because it generally creates confusion that leads to someone running an image through Guetzli twice (or more). Passing an image multiple times through Guetzli is not equivalent to passing it once, and will generate visible artifacts.