- Followup to r325807, with USE_PACKAGE_DEPENDS_ONLY, still allow

ports framework to use the port for *_DEPENDS= ${NONEXISTENT}:PORT:target
  dependencies

  An example port is irc/gseen.mod, it depends on another port being
  extracted, not an installed pkg.

PR:		ports/180725
Reported by:	antoine
With hat:	portmgr

Mk/bsd.port.mk

@@ -4923,7 +4923,7 @@ _INSTALL_DEPENDS=	\
 				else \
 					${PKG_ADD} $${subpkgfile}; \
 				fi; \
-			elif [ -n "${USE_PACKAGE_DEPENDS_ONLY}" ]; then \
+			elif [ -n "${USE_PACKAGE_DEPENDS_ONLY}" -a "$${target}" = "${DEPENDS_TARGET}" ]; then \
 				${ECHO_MSG} "===>   ${PKGNAME} depends on package: $${subpkgfile} - not found"; \
 				${ECHO_MSG} "===>   USE_PACKAGE_DEPENDS_ONLY set - will not build from source"; \
 				exit 1; \