Fix a Panic in admin commands (#779)

We have a panic when we send SHOW or ;;;;;;;;;;;;;;;;; to admin database.

This PR fixes these panics and adds a couple of tests

src/admin.rs

@@ -55,7 +55,12 @@ where
 
     let query_parts: Vec<&str> = query.trim_end_matches(';').split_whitespace().collect();
 
-    match query_parts[0].to_ascii_uppercase().as_str() {
+    match query_parts
+        .first()
+        .unwrap_or(&"")
+        .to_ascii_uppercase()
+        .as_str()
+    {
         "BAN" => {
             trace!("BAN");
             ban(stream, query_parts).await
@@ -84,7 +89,12 @@ where
             trace!("SHUTDOWN");
             shutdown(stream).await
         }
-        "SHOW" => match query_parts[1].to_ascii_uppercase().as_str() {
+        "SHOW" => match query_parts
+            .get(1)
+            .unwrap_or(&"")
+            .to_ascii_uppercase()
+            .as_str()
+        {
             "HELP" => {
                 trace!("SHOW HELP");
                 show_help(stream).await

tests/ruby/admin_spec.rb

@@ -91,6 +91,27 @@ describe "Admin" do
     end
   end
 
+  [
+    "SHOW ME THE MONEY", 
+    "SHOW ME THE WAY", 
+    "SHOW UP", 
+    "SHOWTIME",
+    "HAMMER TIME",
+    "SHOWN TO BE TRUE",
+    "SHOW ",
+    "SHOW     ",
+    "SHOW 1",
+    ";;;;;"
+  ].each do |cmd|
+    describe "Bad command #{cmd}" do
+      it "does not panic and responds with PG::SystemError" do
+        admin_conn = PG::connect(processes.pgcat.admin_connection_string)
+        expect { admin_conn.async_exec(cmd) }.to raise_error(PG::SystemError).with_message(/Unsupported/)
+        admin_conn.close
+      end
+    end
+  end
+
   describe "PAUSE" do
     it "pauses all pools" do
       admin_conn = PG::connect(processes.pgcat.admin_connection_string)