Tell where the colon is missing in the exception message

But sure, it would be surprising if the message was actually displayed
even if the exception is caught and causes some failure
somewhere... (See previous commit.)

Change-Id: I7375b869d08a465d9720a619d5ef49a77c4782e5

configmgr/source/components.cxx

@@ -488,7 +488,7 @@ Components::Components(
         for (;; ++c) {
             if (c == conf.getLength() || conf[c] == ' ') {
                 throw css::uno::RuntimeException(
-                    "CONFIGURATION_LAYERS: missing \":\"");
+                    "CONFIGURATION_LAYERS: missing ':' in \"" + conf + "\"");
             }
             if (conf[c] == ':') {
                 break;