lsp: Fix crash when import version missing

The issue is specific to the language server, since it's trying to use
an AST that contains errors. The test would not fail but was added
anyway.

CONTRIBUTING.md

@@ -0,0 +1,9 @@
+First of all, thank you for contributing to Blueprint.
+
+If you learn something useful, please add it to this file.
+
+# Run the test suite
+
+```
+python -m unittest
+```

blueprintcompiler/language/imports.py

@@ -31,16 +31,17 @@ class GtkDirective(AstNode):
 
     @validate("version")
     def gtk_version(self):
-        if self.tokens["version"] not in ["4.0"]:
+        version = self.tokens["version"]
+        if version not in ["4.0"]:
             err = CompileError("Only GTK 4 is supported")
-            if self.tokens["version"].startswith("4"):
+            if version and version.startswith("4"):
                 err.hint("Expected the GIR version, not an exact version number. Use 'using Gtk 4.0;'.")
             else:
                 err.hint("Expected 'using Gtk 4.0;'")
             raise err
 
         try:
-            gir.get_namespace("Gtk", self.tokens["version"])
+            gir.get_namespace("Gtk", version)
         except CompileError as e:
             raise CompileError(
                 "Could not find GTK 4 introspection files. Is gobject-introspection installed?",

tests/sample_errors/no_import_version.blp

@@ -0,0 +1 @@
+using Gtk 

tests/sample_errors/no_import_version.err

@@ -0,0 +1 @@
+1,10,0,Expected a version number for GTK

tests/test_samples.py

@@ -188,6 +188,7 @@ class TestSamples(unittest.TestCase):
         self.assert_sample_error("gtk_exact_version")
         self.assert_sample_error("invalid_bool")
         self.assert_sample_error("layout_in_non_widget")
+        self.assert_sample_error("no_import_version")
         self.assert_sample_error("ns_not_imported")
         self.assert_sample_error("not_a_class")
         self.assert_sample_error("object_dne")