Fix attempted recovery from corrupted b_info

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=66271&q=label%3AProj-upx
	modified:   p_lx_elf.cpp

src/p_lx_elf.cpp

@@ -8618,7 +8618,7 @@ void PackLinuxElf32::unpack(OutputFile *fo)
                         }
                     }
                     int boff = find_le32(peek_arr, sizeof(peek_arr), size);
-                    if (boff < 0) {
+                    if (boff < 0 || sizeof(peek_arr) < (sizeof(*bp) + boff)) {
                         throwCantUnpack("b_info corrupted");
                     }
                     bp = (b_info *)(void *)&peek_arr[boff];