A struct_decl_idx of zero is valid - fixes abort in test1.
A struct_decl_idx of zero is valid - fixes abort in test1.

mstorsjo/c99-to-c89,libav/c99-to-c89,libav/c99-to-c89,rbultje/c99-to-c89,rbultje/c99-to-c89,mstorsjo/c99-to-c89