Revert "patch: fix pch_context() for unified diffs with no leading context"

This reverts commit f97b6a8, as it
turns out our fuzz implementation is just too naive.  We can have more
leading context than trailing context and vice-versa, so we can't really
assume they're the same.

Restore the previous bug and we can work on it post-branch.

Reported by:	cy

Author: kevans91

usr.bin/patch/pch.c

@@ -1054,7 +1054,7 @@ another_hunk(void)
 				p_end = fillnew;
 				malformed();
 			}
-			if (ch != ' ' && context >= 0) {
+			if (ch != ' ' && context > 0) {
 				if (context < p_context)
 					p_context = context;
 				context = -1000;

usr.bin/patch/tests/unified_patch_test.sh

@@ -25,26 +25,6 @@
 # SUCH DAMAGE.
 #
 
-atf_test_case badfuzz
-badfuzz_head()
-{
-	atf_set "descr" "Test for patch(1) erroneously fuzzing away action lines"
-}
-badfuzz_body()
-{
-	# PR 250511 demonstrates a scenario where patch(1) will happily apply a
-	# patch into the wrong location if we have some lines that are still
-	# similar in the trailing context.  In the following example, it would
-	# actually replace the underscore before the second series of B\nC\nO
-	# with "Z", when the patch should have been rejected instead.
-	printf "A\nB\nC\nO\n_\nB\nC\nO\n" > file.orig
-	printf "Z\nB\nC\nO\n_\nB\nC\nO\n" > file
-	printf "OK\nDIFF1\nDIFF2\n\n_\nB\nC\nO\n" > file.newer
-
-	atf_check -s not-exit:0 -o save:file.patch diff -u3 file.orig file
-	atf_check -s not-exit:0 -o not-empty patch file.newer file.patch
-}
-
 atf_test_case basic
 basic_body()
 {
@@ -198,7 +178,6 @@ EOF
 
 atf_init_test_cases()
 {
-	atf_add_test_case badfuzz
 	atf_add_test_case basic
 	atf_add_test_case limited_ctx
 	atf_add_test_case file_creation