unpackExtent detects corrupted compression method

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=66338&q=label%3AProj-upx
	modified:   p_unix.cpp

src/p_unix.cpp

@@ -481,7 +481,7 @@ unsigned PackUnix::unpackExtent(unsigned wanted, OutputFile *fo,
         int const sz_cpr = ph.c_len = get_te32(&hdr.sz_cpr);
         ph.filter_cto = hdr.b_cto8;
 
-        if (sz_unc == 0) { // must never happen while 0!=wanted
+        if (sz_unc == 0 || M_LZMA < hdr.b_method) {
             throwCantUnpack("corrupt b_info");
             break;
         }