po-docs: Run po4a-translate and sed commands separately

I noticed that 1-byte translated POD files were being generated in the
output directory (po-docs/ja/).  This seems to have happened because
po4a-translate was generating an error, but because we were
immediately pipeing the output into sed the error was suppressed.

By running them as two separate commands this cannot happen.

Fixes: commit bd896d6

po-docs/language.mk

@@ -179,13 +179,16 @@ virt-p2v.1: virt-p2v.pod virt-p2v-kernel-config.pod
 # Remove both.
 # XXX Fix po4a so it doesn't do this.
 %.pod: $(srcdir)/../$(LINGUA).po
+	rm -f $@ $@-t
 	$(guestfs_am_v_po4a_translate)$(PO4A_TRANSLATE) \
 	  -f pod \
 	  -M utf-8 -L utf-8 \
 	  -k 0 \
 	  -m $(top_srcdir)/$(shell grep '/$(notdir $@)$$' $(top_srcdir)/po-docs/podfiles) \
 	  -p $< \
-	  | $(SED) '0,/^=encoding/d' > $@
+	  -l $@-t
+	$(SED) '0,/^=encoding/d' < $@-t > $@
+	rm $@-t
 
 # XXX Can automake do this properly?
 install-data-hook: