graphics/gimp-app: Fix build with librsvg2-rust 2.58.90+

Fix suggested by mikael@ and adapted by fluffy@

Reference:
https://gitlab.gnome.org/GNOME/librsvg/-/blob/2.58.91/NEWS?ref_type=tags

Patch sent privately via Matrix

PR:		284977
Tested by:	fluffy
Approved by:	portmgr (blanket, build fix)

graphics/gimp-app/Makefile

 PORTNAME=	gimp
 DISTVERSION=	2.10.38
-PORTREVISION=	3
+PORTREVISION=	4
 PORTEPOCH=	1
 CATEGORIES=	graphics gnome
 MASTER_SITES=	GIMP/gimp/v${PORTVERSION:R}
@@ -132,6 +132,7 @@ post-patch:
 			${WRKSRC}/plug-ins/pygimp/Makefile.in
 	@${REINPLACE_CMD} \
 		-e 's|x86_64|amd64|g' \
+		-e 's|libpixbufloader-svg.so|libpixbufloader_svg.so|g' \
 		${WRKSRC}/configure.ac
 
 .include <bsd.port.mk>