Clean up stale editor-hInstance comments, add isOwnModulePath edge tests

Drops a false claim about ReaSampler's own editor's hInstance, corrects the real reason for registering the wndproc class against our own module, and covers isOwnModulePath's separator edge cases.

tests/test_window_origin.cpp

@@ -194,6 +194,18 @@ static void testOwnModulePathStableAndBetaDoNotMatchEachOther() {
     CHECK(!isOwnModulePath("C:\\VST3\\reasampler_9000.vst3", "reasampler_9000_beta.vst3"));
 }
 
+static void testOwnModulePathBareFilenameWithNoSeparatorMatches() {
+    CHECK(isOwnModulePath("reasampler_9000.vst3", "reasampler_9000.vst3"));
+}
+
+static void testOwnModulePathEmptyPathDoesNotMatch() {
+    CHECK(!isOwnModulePath("", "reasampler_9000.vst3"));
+}
+
+static void testOwnModulePathTrailingSeparatorDoesNotMatch() {
+    CHECK(!isOwnModulePath("C:\\VST3\\reasampler_9000.vst3\\", "reasampler_9000.vst3"));
+}
+
 int main() {
     testHostExecutableIsHost();
     testOsModulesAreSystem();
@@ -216,6 +228,9 @@ int main() {
     testOwnModulePathCaseFolds();
     testOwnModulePathBundlePathForwardAndBackSlash();
     testOwnModulePathStableAndBetaDoNotMatchEachOther();
+    testOwnModulePathBareFilenameWithNoSeparatorMatches();
+    testOwnModulePathEmptyPathDoesNotMatch();
+    testOwnModulePathTrailingSeparatorDoesNotMatch();
 
     if (g_fail == 0) std::printf("All tests passed.\n");
     return g_fail ? 1 : 0;