Experimental parser: fix off by one error in utf8 decoding

tools/lexer_generator/code_generator.jinja

 #include "lexer/experimental-scanner.h"
 
 {%- macro do_key(key) -%}
   {%- for r in key -%}
     {%- if not loop.first %} || {% endif -%}
     {%- if r[0] == 'PRIMARY_RANGE' -%}
       {%- if r[1][0] == r[1][1] -%}
         primary_char == {{r[1][0]}}
       {%- elif r[1][0] == 0 -%}
         primary_char <= {{r[1][1]}}
@@ skipping 76 matching lines @@
 
 {%- macro long_char_create() -%}
   {%- if encoding == 'utf16'-%}
     const uint32_t long_char = primary_char;
   {%- elif encoding == 'utf8'-%}
     unsigned bytes_read = 0;
     const uint32_t long_char = unibrow::Utf8::CalculateValue(
         reinterpret_cast<uint8_t*>(cursor_),
         buffer_end_ - cursor_,
         &bytes_read);
-    cursor_ += bytes_read;
+    cursor_ += bytes_read - 1;
     if (long_char == unibrow::Utf8::kBadChar) goto default_action;
   {%- else -%}
     uncompilable code for {{encoding}}
   {%- endif -%}
 {%- endmacro -%}
 
 
 {%- macro do_dfa_state(node_number, inline) -%}
 
   {%- set state = dfa_states[node_number] -%}
@@ skipping 151 matching lines @@
 {% endif -%}
     {{dispatch_action(default_action[0], default_action[1])}}
   FORWARD();
   goto code_start;
 
   fell_through:
   CHECK(false);
 }
 } }