gnu: grep: Apply fix for CVE-2015-1345.

* gnu/packages/patches/grep-CVE-2015-1345.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/base.scm (grep): Add patch.

gnu/packages/patches/grep-CVE-2015-1345.patch

@@ -0,0 +1,17 @@
+Fix CVE-2015-1345.  From upstream commit
+83a95bd8c8561875b948cadd417c653dbe7ef2e2
+by Yuliy Pisetsky <ypisetsky@fb.com>.
+
+diff --git a/src/kwset.c b/src/kwset.c
+index 4003c8d..376f7c3 100644
+--- a/src/kwset.c
++++ b/src/kwset.c
+@@ -643,6 +643,8 @@ bmexec_trans (kwset_t kwset, char const *text, size_t size)
+                     if (! tp)
+                       return -1;
+                     tp++;
++                    if (ep <= tp)
++                      break;
+                   }
+               }
+           }