Fix up the previous commit

Fallout from d6f0488665

Dockerfile

@@ -26,4 +26,18 @@ COPY extra-packages /
 RUN dnf -y install $(<extra-packages)
 RUN rm /extra-packages
 
+COPY ensure-files /
+RUN ret_val=0; \
+  while read file; do \
+    if ! compgen -G "$file" >/dev/null; then \
+      echo "$file: No such file or directory" >&2; \
+      ret_val=1; \
+      break; \
+    fi; \
+  done <ensure-files; \
+  if [ "$ret_val" -ne 0 ]; then \
+    false; \
+  fi
+RUN rm /ensure-files
+
 RUN dnf clean all