pkgconfig generator: Fix crash when passing a SharedModule

mesonbuild/modules/pkgconfig.py

@@ -87,6 +87,7 @@ class DependenciesHelper:
         processed_reqs = []
         processed_cflags = []
         for obj in libs:
+            shared_library_only = getattr(obj, 'shared_library_only', False)
             if hasattr(obj, 'pcdep'):
                 pcdeps = mesonlib.listify(obj.pcdep)
                 for d in pcdeps:
@@ -105,7 +106,7 @@ class DependenciesHelper:
                 if obj.found():
                     processed_libs += obj.get_link_args()
                     processed_cflags += obj.get_compile_args()
-            elif isinstance(obj, build.SharedLibrary) and obj.shared_library_only:
+            elif isinstance(obj, build.SharedLibrary) and shared_library_only:
                 # Do not pull dependencies for shared libraries because they are
                 # only required for static linking. Adding private requires has
                 # the side effect of exposing their cflags, which is the