Return null instead of throwing if a file is not found in sources

The primary use case for open_from_sources is for creator functions to
open raw files.  This change makes it easier to gracefully skip a non-
existent file and carry on with other ways of loading the item.

diff --git a/source/collection.cpp b/source/collection.cpp
index 984fb74da8e7a6007645e6f85aa002b8ae6f894a..aa607bdedcde65ecfd298b21af06fc9dc42aeac2 100644 (file)
--- a/source/collection.cpp
+++ b/source/collection.cpp
@@ -97,7 +97,7 @@ IO::Seekable *Collection::open_from_sources(const string &name)
                if(IO::Seekable *io = (*i)->open(name))
                        return io;
 
-       throw IO::file_not_found(name);
+       return 0;
 }
 
 void Collection::gather_names_from_sources(list<string> &names, const CollectionItemTypeBase &type) const