File selection cancel logic added

[knowblesse]

In current version, 9398cac, the gui.io module uses qtpy.QtWidgets.QFileDialog to prompt the user for an input image.

cellpose/cellpose/gui/io.py

Line 108 in 9398cac

name = QFileDialog.getOpenFileName(parent, "Load image")

However, if the user cancels the file selection, QFileDialog returns an empty string, which is then passed to imread at line 125.

cellpose/cellpose/gui/io.py

Lines 125 to 126 in 9398cac

	image = imread(filename)
	parent.loaded = True

Since imread has its own error handling, all exceptions are suppressed, and line 126 (parent.loaded = True) is executed even if no file is selected.

This behavior is undesired, so a simple filename check has been added to return from the _load_image function without setting parent.loaded to True if no file is selected.

[knowblesse]

It's just a minor error, but since parent.loaded is used widely throughout the code, it might cause unexpected behavior in other cases.