scripts/git: Restore a dropped check for pre-commit in pre-push

Bugfix on 31919; not in any released version of Tor.

scripts/git/pre-push.git-hook

@@ -58,35 +58,39 @@ do
         fi
 
         # Call the pre-commit hook for the common checks, if it is executable
-        # Only check the files newly modified in this branch
-        CHECK_FILTER="git diff --name-only --diff-filter=ACMR $range"
-        # Use the appropriate owned tor source list to filter the changed files
-        if [ -d src/lib ]; then
-            # This is the layout in 0.3.5
-            CHECK_FILES="$($CHECK_FILTER \
-                               src/lib/*/*.[ch] \
-                               src/core/*/*.[ch] \
-                               src/feature/*/*.[ch] \
-                               src/app/*/*.[ch] \
-                               src/test/*.[ch] \
-                               src/test/*/*.[ch] \
-                               src/tools/*.[ch] \
-                          )"
-        elif [ -d src/common ]; then
-            # This was the layout before 0.3.5
-            CHECK_FILES="$($CHECK_FILTER \
-                               src/common/*/*.[ch] \
-                               src/or/*/*.[ch] \
-                               src/test/*.[ch] \
-                               src/test/*/*.[ch] \
-                               src/tools/*.[ch]
-                          )"
-        fi
+        if [ -x scripts/git/pre-commit.git-hook ]; then
+            # Only check the files newly modified in this branch
+            CHECK_FILTER="git diff --name-only --diff-filter=ACMR $range"
+            # Use the appropriate owned tor source list to filter the changed
+            # files
+            if [ -d src/lib ]; then
+                # This is the layout in 0.3.5
+                CHECK_FILES="$($CHECK_FILTER \
+                                   src/lib/*/*.[ch] \
+                                   src/core/*/*.[ch] \
+                                   src/feature/*/*.[ch] \
+                                   src/app/*/*.[ch] \
+                                   src/test/*.[ch] \
+                                   src/test/*/*.[ch] \
+                                   src/tools/*.[ch] \
+                              )"
+            elif [ -d src/common ]; then
+                # This was the layout before 0.3.5
+                CHECK_FILES="$($CHECK_FILTER \
+                                   src/common/*/*.[ch] \
+                                   src/or/*/*.[ch] \
+                                   src/test/*.[ch] \
+                                   src/test/*/*.[ch] \
+                                   src/tools/*.[ch]
+                              )"
+            fi
 
-        # We want word splitting here, because file names are space separated
-        # shellcheck disable=SC2086
-        if ! scripts/git/pre-commit.git-hook $CHECK_FILES ; then
-            exit 1
+            # We want word splitting here, because file names are space
+            # separated
+            # shellcheck disable=SC2086
+            if ! scripts/git/pre-commit.git-hook $CHECK_FILES ; then
+                exit 1
+            fi
         fi
 
         if [[ "$remote_name" != "$upstream_name" ]]; then