Use of "throw 0" as flow-control

[Paul J. Lucas]

In loader_dtd.cpp for the loadXml() function, "throw 0" is used as "flow control" for the function. This is not an appropriate use of C++ exceptions. The very real danger is that the corresponding "catch (...)" swallows all other exceptions silently. This causes very hard-to-find bugs (as I recently had the misfortune of debugging).

The rule should be that if you ever write "catch (...)," the end of the catch block should ALWAYS rethrow the exception via "throw;". The catch block in this way only does some clean-up but makes no attempt to swallow the exception.

Please don't use "throw 0" with "catch (...)". Even using "goto" is better since it won't silently swallow exceptions.

Note that I have already cleaned up several other uses of "catch (...)" in the code (see bug #1103819). This bug is a related bug in that it's about the (mis)use of "catch (...)" but specifically a case I don't feel comfortable fixing myself. There is already a branch for all "catch (...)" fixes -- please use the bug-1103819 branch.