Don't modify blocks in template processors

lib/brakeman/processors/erb_template_processor.rb

@@ -56,6 +56,7 @@ class Brakeman::ErbTemplateProcessor < Brakeman::TemplateProcessor
 
   #Process block, removing irrelevant expressions
   def process_block exp
+    exp = exp.dup
     exp.shift
     if @inside_concat
       @inside_concat = false

lib/brakeman/processors/erubis_template_processor.rb

@@ -55,6 +55,7 @@ class Brakeman::ErubisTemplateProcessor < Brakeman::TemplateProcessor
 
   #Process blocks, ignoring :ignore exps
   def process_block exp
+    exp = exp.dup
     exp.shift
     exp.map! do |e|
       res = process e

lib/brakeman/processors/haml_template_processor.rb

@@ -103,6 +103,7 @@ class Brakeman::HamlTemplateProcessor < Brakeman::TemplateProcessor
 
   #If inside an output stream, only return the final expression
   def process_block exp
+    exp = exp.dup
     exp.shift
     if @inside_concat
       @inside_concat = false