Avoid extra composer.json files at build

Patching composer.json creates extra composer.json files in the .pc/
directory. During the build we search for composer.json files. Errors
occur in subsequent builds if a file in .pc/ is found and parsed after
the intended one in the source tree.

Limit the selection of composer.json files to the known locations: in
the project root and in the component directories in src/.

debian/rules

@@ -56,7 +56,7 @@ debian/%.autoload.php.tpl: debian/%.buildvars
 
 $(packages:%=debian/%.buildvars):
 	set -e ;\
-	for composer in $$(find -name composer.json -printf '%P\n'); do \
+	for composer in composer.json $(wildcard src/*/*/composer.json); do \
 		package=$$(jq -r .name $$composer | sed 's:^:php-:;s:/:-:g') ;\
 		sourcedir=$$(dirname $$composer) ;\
 		echo "sourcedir=$$sourcedir" >debian/$$package.buildvars ;\