init: fix unescape_string not advancing past escape characters

After processing a \X escape sequence in the switch block, the read
pointer (val) was not advanced past the matched character. The next
loop iteration re-processed it as a literal, producing a spurious
extra byte for every escape sequence.
For example, JSON "\n" decoded to {0x0A, 'n'} instead of {0x0A},
and JSON "\\" decoded to {'\', <next char interpreted as escape>}
instead of {'\'}.
Also fix the \u case: hexToDigit was called with a pointer to 'u'
instead of the first hex digit (val++ vs ++val), and the write index
was not advanced after memcpy, so decoded Unicode characters were
silently dropped. This caused e.g. \u0026 ('&') to be lost, breaking
any container command containing '&&'.

Author: nikromen

init/init.c

@@ -666,7 +666,8 @@ static void unescape_string(char *string, int len)
             const char *unescaped = "?";
             char utf8Buf[5];
             unsigned int codepoint = 0;
-            hexToDigit(&codepoint, val++);
+            /* skip 'u', point at first hex digit */
+            hexToDigit(&codepoint, ++val);
             val += 3;
             /* check if this is a surrogate */
             if ((codepoint & 0xFC00) == 0xD800) {
@@ -692,9 +693,11 @@ static void unescape_string(char *string, int len)
                 continue;
             }
             memcpy(&string[i], unescaped, (unsigned int)strlen(unescaped));
+            i += strlen(unescaped);
             break;
         }
         }
+        val++;
     }
     string[i] = '\0';
 }