Initialize local variable

In `aztec_text_process`, `binary_string`, which aliases to `aztec`'s
`bit_pattern` has it's first element set to NUL. However, when the string
is later written into using `bin_append_posn`, that NUL is overwritten and
further NUL to replace it is not appended.

In general, the garbage collected memory content should never be assumed to
have a specific value unless a value was explicitly assigned, so the content
of `bit_pattern` cannot be safely assumed to be NUL.

If the string is not NUL terminated, functions relying on NUL termination,
such as the printf call at the end of `aztec_text_proccess` itself,
will overrun the array bounds.

Explicitly initialize `bit_pattern`

backend/aztec.c

@@ -852,6 +852,7 @@ INTERNAL int aztec(struct zint_symbol *symbol, unsigned char source[], int lengt
 #endif
 
     memset(adjusted_string, 0, AZTEC_MAX_CAPACITY);
+    memset(bit_pattern, 0, AZTEC_MAP_POSN_MAX + 1);
 
     if ((symbol->input_mode & 0x07) == GS1_MODE) {
         gs1 = 1;