Check springsettings reading func

[sprunk]

spring/rts/System/Config/ConfigSource.cpp

Lines 58 to 69 in ab88be7

	if ((file = fopen(filename.c_str(), "r"))) {
	ScopedFileLock scoped_lock(fileno(file), false);
	Read(file);
	fclose(file);
	}
	else if ((file = fopen(filename.c_str(), "a"))) {
	// TODO: write some initial contents into the config file?
	fclose(file);
	}
	else {
	LOG_L(L_ERROR, "FileConfigSource: Error: Could not write to config file \"%s\"", filename.c_str());
	}

AFAICT this is supposed to just open the file (specifically springsettings.cfg) for reading. I think that:

• if the file doesn't exist, then "r" will fail and it is fine, and creating it via "a" is fine. It could produce a notice-level log.
• if the file exists but fails to be read there should be an error message (ideally with reason like "permissions"). Retrying via "a" is probably fine but idk if there is ever a case where that would help.
• if both methods fail the existing error log should say "could not read" and not "write".