Add missing char identification

Author: xCollateral

src/main/java/net/vulkanmod/vulkan/shader/converter/Lexer.java

@@ -150,7 +150,7 @@ public Token nextToken() {
         };
 
         if (token == null) {
-            if (Character.isLetter(currentChar)) {
+            if (Character.isLetter(currentChar) || currentChar == '_') {
                 return identifier();
             }