glsl2: Fix warning from always-false assert not being known to not return.
diff --git a/src/glsl/glsl_parser_extras.cpp b/src/glsl/glsl_parser_extras.cpp
index fc3f9e9..cb7b6d3 100644
--- a/src/glsl/glsl_parser_extras.cpp
+++ b/src/glsl/glsl_parser_extras.cpp
@@ -45,6 +45,7 @@
    }
 
    assert(!"Should not get here.");
+   return "unknown";
 }