refspec: a ref name includes the refs/ prefix

git_refspec_transform_r assumed that the reference name passed would
be only a branch or tag name. This is not the case, and we need to
take into consideration what's in the refspec's source to know how
much of the prefix to ignore.

src/refspec.c

@@ -107,7 +107,7 @@ int git_refspec_transform_r(git_buf *out, const git_refspec *spec, const char *n
 		return GIT_SUCCESS;
 
 	git_buf_truncate(out, out->size - 1); /* remove trailing '*' */
-	git_buf_puts(out, name);
+	git_buf_puts(out, name + strlen(spec->src) - 1);
 
 	return git_buf_lasterror(out);
 }

tests-clar/network/remotes.c

 #include "clar_libgit2.h"
+#include "buffer.h"
+#include "refspec.h"
 
 static git_remote *_remote;
 static git_repository *_repo;
@@ -48,3 +50,11 @@ void test_network_remotes__transform(void)
 	cl_git_pass(git_refspec_transform(ref, sizeof(ref), _refspec, "refs/heads/master"));
 	cl_assert(!strcmp(ref, "refs/remotes/test/master"));
 }
+
+void test_network_remotes__transform_r(void)
+{
+	git_buf buf = GIT_BUF_INIT;
+
+	cl_git_pass(git_refspec_transform_r(&buf,  _refspec, "refs/heads/master"));
+	cl_assert(!strcmp(git_buf_cstr(&buf), "refs/remotes/test/master"));
+}