Fix null pointer crash in tokenDelete function

The tokenDelete() function in main/tokeninfo.c was being called with NULL
pointers from the R6 parser error handling code, causing segmentation faults.

The R6 parser in parsers/r-r6class.c had a comment stating "tokenDelete
accepts NULL" but the function did not actually handle NULL pointers safely.
This occurred when parsing malformed R6 syntax such as:
- R6::SomethingElse() (wrong function after R6 namespace)
- R6:: (incomplete namespace reference)
- R6::R6Clas() (typo in R6Class)

The fix ensures ctags handles malformed R6 syntax gracefully by falling back
to parsing assignments as regular global variables instead of crashing.

  Fixes segmentation fault when processing certain R6Class syntax patterns.

Signed-off-by: Bernát Gábor <[email protected]>

Author: gaborbernat

Units/parser-r6class.r/r6-null-pointer-regression.d/args.ctags

@@ -0,0 +1,3 @@
+--sort=no
+--fields=+ilaKSe{extras}
+--extras=-p

Units/parser-r6class.r/r6-null-pointer-regression.d/expected.tags

@@ -0,0 +1,3 @@
+TestCase1	Units/parser-r6class.r/r6-null-pointer-regression.d/input.r	/^TestCase1 <- R6::SomethingElse("TestCase1")$/;"	globalVar	language:R	end:6
+TestCase2	Units/parser-r6class.r/r6-null-pointer-regression.d/input.r	/^TestCase2 <- R6::$/;"	globalVar	language:R	end:10
+TestCase3	Units/parser-r6class.r/r6-null-pointer-regression.d/input.r	/^TestCase3 <- R6::R6Clas("TestCase3")/;"	globalVar	language:R	end:12

Units/parser-r6class.r/r6-null-pointer-regression.d/input.r

@@ -0,0 +1,12 @@
+# Test case for R6 parser null pointer regression
+# This triggers the error path in r6ReadRightSideSymbol that was causing
+# tokenDelete to be called with NULL pointers
+
+# Case 1: R6:: followed by something other than R6Class
+TestCase1 <- R6::SomethingElse("TestCase1")
+
+# Case 2: Incomplete R6 namespace reference
+TestCase2 <- R6::
+
+# Case 3: R6 followed by :: but with syntax error
+TestCase3 <- R6::R6Clas("TestCase3")

main/tokeninfo.c

@@ -91,7 +91,8 @@ void  flashTokenBacklog (struct tokenInfoClass *klass)
 
 void tokenDelete (tokenInfo *token)
 {
-	objPoolPut (token->klass->pool, token);
+	if (token != NULL)
+		objPoolPut (token->klass->pool, token);
 }