Keep spaces in a COLMAP image name

[SashaMIT]

Summary

• read_images_text kept only the first word of the image name. my photo.jpg came back as my.
• COLMAP writes the name as the rest of the line, so a space is part of the filename. The points on the next line are unchanged.
• A name with no space, such as plain.jpg, still comes back as plain.jpg.

Test plan

• test_image_name_keeps_spaces: my photo.jpg stays intact, point id 7 stays 7, and plain.jpg is unchanged