"Cannot open source file" errors on missing headers no longer appear with 1.19.9 with C_Cpp.errorSquiggles set to "enabled"

[sean-mcmanus]

Repro is to set C_Cpp.errorSquiggles to "enabled" instead of the default of "enabledIfIncludesResolve" and

#include <donotexist.h>

// enter as many newlines as required to make the "int i;" not visible. 
int i;

i.e. the bug requires there be some code that is not visible on the screen.

It works with 1.18.5.

Bug2: With enabledIfIncludesResolve, it only shows 1 missing include error at a time and the shown error can change depend on where the last IntelliSense update occurred.