fix dynamic linker regression processing R_*_NONE type relocations

commit f3ddd17380 inadvertently removed
the early check for "none" type relocations, causing the address
dso->base+0 to be dereferenced to obtain an addend. shared libraries,
(including libc.so) and PIE executables were unaffected, since their
base addresses are the actual address of their mappings and are
readable. non-PIE main executables, however, have a base address of 0
because their load addresses are absolute and not offset at load time.

in practice none-type relocations do not arise with toolchains that
are in use except on mips, and on mips it's moderately rare for a
non-PIE executable to have a relocation table, since the mips-specific
got processing serves in its place for most purposes.

src/ldso/dynlink.c

@@ -270,6 +270,7 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri
 	for (; rel_size; rel+=stride, rel_size-=stride*sizeof(size_t)) {
 		if (skip_relative && IS_RELATIVE(rel[1])) continue;
 		type = R_TYPE(rel[1]);
+		if (type == REL_NONE) continue;
 		sym_index = R_SYM(rel[1]);
 		reloc_addr = (void *)(base + rel[0]);
 		if (sym_index) {