17298 Windows agent reports the version of custom exe plugin as n/a

For any exe plugin except for mk-sql.exe, the version is reported as n/a.
For mk-sql.exe, its actual version is reported.

Change-Id: Ifdafc4c28f87400e3d51f483687e1a876948502d

.werks/17298.md

@@ -0,0 +1,15 @@
+[//]: # (werk v2)
+# Windows agent reports the version of custom exe plugin as n/a
+
+key        | value
+---------- | ---
+date       | 2025-01-14T07:58:04+00:00
+version    | 2.4.0b1
+class      | feature
+edition    | cre
+component  | checks
+level      | 1
+compatible | yes
+
+For any exe plugin except for mk-sql.exe, the version is reported as n/a. 
+For mk-sql.exe, its actual version is reported.

agents/wnx/src/engine/providers/agent_plugins.cpp

@@ -87,6 +87,8 @@ std::string FindVersionInfo(const fs::path &file, FileType file_type) {
                         return fmt::format("{}:CMK_VERSION = \"{}\"", file,
                                            output[1]);
                     }
+                } else {
+                    return fmt::format("{}:CMK_VERSION = n/a", file);
                 }
                 return {};
             }

agents/wnx/watest/test-section_agent_plugins.cpp

@@ -57,6 +57,16 @@ TEST_F(AgentPluginsTest, File) {
     }));
 }
 
+TEST_F(AgentPluginsTest, JustExe) {
+    auto ps_file = fs::path{cfg::GetUserPluginsDir()} / "empty.exe";
+    tst::CreateTextFile(ps_file, "");
+    auto rows = getRows();
+    ASSERT_EQ(rows.size(), 4);
+    EXPECT_TRUE(std::ranges::any_of(rows, [&](const std::string &row) {
+        return row == fmt::format("{}:CMK_VERSION = n/a", ps_file);
+    }));
+}
+
 TEST_F(AgentPluginsTest, DISABLED_Exe) {
     // Test is disabled because we need a binary to build: not appropriate for
     // unit testing. You may enable this test manually