[ASan] Fix coverage behavior when a PC belongs to an unknown address range.

This happens, e.g., when coverage data is collected for a module which is then
dlclose()'d. Currently this causes CovDump() to ignore all PCs that are greater
than the unrecognized PC. In other words, unloading a module causes ASan to
silently ignore any coverage data for modules loaded at higher addresses.
Instead we should just skip the unrecognized PCs.