bugfix: don't look up patches from packages for concrete specs

The concretizer can fail with `reuse:true` if a buildcache or installation contains a
package with a dependency that has been renamed or deleted in the main repo (e.g.,
`netcdf` was refactored to `netcdf-c`, `netcdf-fortran`, etc., but there are still
binary packages with dependencies called `netcdf`).

We should still be able to install things for which we are missing `package.py` files.

`Spec.inject_patches_variant()` was failing this requirement by attempting to look up
the package class for concrete specs.  This isn't needed -- we can skip it.

- [x] swap two conditions in `Spec.inject_patches_variant()`

lib/spack/spack/spec.py

@@ -2789,11 +2789,11 @@ def inject_patches_variant(root):
         # Also record all patches required on dependencies by
         # depends_on(..., patch=...)
         for dspec in root.traverse_edges(deptype=all, cover="edges", root=False):
-            pkg_deps = dspec.parent.package_class.dependencies
-            if dspec.spec.name not in pkg_deps:
+            if dspec.spec.concrete:
                 continue
 
-            if dspec.spec.concrete:
+            pkg_deps = dspec.parent.package_class.dependencies
+            if dspec.spec.name not in pkg_deps:
                 continue
 
             patches = []