pe-binary: add explicit cast to silence coverity

Otherwise it gets confused about underflows (which are already checked)

CID#1645068

Follow-up for a434270139

src/shared/pe-binary.c

@@ -423,7 +423,7 @@ int pe_hash(int fd,
                 if ((uint64_t) st.st_size - p < le32toh(certificate_table->Size))
                         return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG), "No space for certificate table, refusing.");
 
-                r = hash_file(fd, mdctx, p, st.st_size - p - le32toh(certificate_table->Size));
+                r = hash_file(fd, mdctx, p, (uint64_t) st.st_size - p - le32toh(certificate_table->Size));
                 if (r < 0)
                         return r;