Null terminate the std::array given to execve

std::array<T, N> takes exactly N * sizeof(T) bytes, leaving no room for
the null terminator.

Bug: 335047945
Test: re-run the GSI test
Change-Id: Ic3aca5f409021c78a7eb965c5ed610e6a51e42cb
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index ae216c6..5d3a273 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -556,11 +556,11 @@
         return true;
     }
     // clang-format off
-    const std::array<const char*, 7> args = {
+    const std::array<const char*, 8> args = {
         "/system/bin/derive_microdroid_vendor_dice_node",
                 "--dice-driver", "/dev/open-dice0",
                 "--microdroid-vendor-disk-image", microdroid_vendor_block_dev->data(),
-                "--output", "/microdroid_resources/dice_chain.raw",
+                "--output", "/microdroid_resources/dice_chain.raw", nullptr,
     };
     // clang-format-on
     // ForkExecveAndWaitForCompletion calls waitpid to wait for the fork-ed process to finish.