ncsixel_as_rgba: fix processing following '$'

waveplate pointed out that we needed to move to
STATE_WANT_DATA rather than STATE_WANT_HASH following
a '$' in sixel text. this was breaking ncsixel_as_rgba()
for larger sixels, for which we now have a unit test.

Closes #2784

NEWS.md

@@ -5,6 +5,10 @@ rearrangements of Notcurses.
   * We now normalize the return of `nl_langinfo()` according to the behavior
     of glibc's `_nl_normalize_charset()`, supporting some atypical synonyms
     of `UTF-8`.
+  * Fixed a bug in `ncsixel_as_rgba()` (called by `ncvisual_from_sixel()`)
+    that broke loading of sixels having more than 12 rows (sixel generation
+    from images worked fine). Thanks, waveplate!
+  * Reject illegal geometries in `ncvisual_from_*()`.
 
 * 3.0.9 (2022-12-10)
   * Eliminated infinite loop in `ncplane_move_family_above()`.

src/lib/sixel.h

@@ -10,6 +10,10 @@ extern "C" {
 #include "logging.h"
 
 uint32_t* ncsixel_as_rgba(const char *sx, unsigned leny, unsigned lenx){
+  if(!leny || !lenx){
+    logerror("null sixel geometry");
+    return NULL;
+  }
 #define MAXCOLORS 65535
   // cast is necessary for c++ callers
   uint32_t* rgba = (uint32_t*)calloc(leny * lenx, sizeof(*rgba));
@@ -26,7 +30,7 @@ uint32_t* ncsixel_as_rgba(const char *sx, unsigned leny, unsigned lenx){
   // transparent line (the only possible colorless line).
   while(*sx != '#' && *sx != '-'){
     if(!*sx){
-      logerror("expected octothorpe/hyphen, got eol\n");
+      logerror("expected octothorpe/hyphen, got eol");
       return NULL;
     }
     ++sx;
@@ -56,12 +60,12 @@ uint32_t* ncsixel_as_rgba(const char *sx, unsigned leny, unsigned lenx){
       }else if('#' == *sx){
         state = STATE_WANT_COLOR;
       }else{
-        logerror("expected octothorpe, got %u\n", *sx);
+        logerror("expected octothorpe, got %u", *sx);
         goto err;
       }
     }else if(state == STATE_WANT_COLOR){
       if(!isdigit(*sx)){
-        logerror("expected digit, got %u\n", *sx);
+        logerror("expected digit, got %u", *sx);
         goto err;
       }
       color = 0;
@@ -84,12 +88,12 @@ uint32_t* ncsixel_as_rgba(const char *sx, unsigned leny, unsigned lenx){
       }
     }else if(state == STATE_WANT_COLORSPACE){
       if('2' != *(sx++)){
-        logerror("expected '2', got %u\n", *sx);
+        logerror("expected '2', got %u", *sx);
         goto err;
       }
 //fprintf(stderr, "SX: %u 0x%02x %c\n", *sx, *sx, *sx);
       if(';' != *(sx++)){
-        logerror("expected semicolon, got %u\n", *sx);
+        logerror("expected semicolon, got %u", *sx);
         goto err;
       }
 //fprintf(stderr, "SX: %u 0x%02x %c\n", *sx, *sx, *sx);
@@ -100,7 +104,7 @@ uint32_t* ncsixel_as_rgba(const char *sx, unsigned leny, unsigned lenx){
         ++sx;
       }while(isdigit(*sx));
       if(';' != *(sx++)){
-        logerror("expected semicolon, got %u\n", *sx);
+        logerror("expected semicolon, got %u", *sx);
         goto err;
       }
 //fprintf(stderr, "SX: %u 0x%02x %c\n", *sx, *sx, *sx);
@@ -112,7 +116,7 @@ uint32_t* ncsixel_as_rgba(const char *sx, unsigned leny, unsigned lenx){
         ++sx;
       }while(isdigit(*sx));
       if(';' != *(sx++)){
-        logerror("expected semicolon, got %u\n", *sx);
+        logerror("expected semicolon, got %u", *sx);
         goto err;
       }
 //fprintf(stderr, "SX: %u 0x%02x %c\n", *sx, *sx, *sx);
@@ -153,7 +157,7 @@ uint32_t* ncsixel_as_rgba(const char *sx, unsigned leny, unsigned lenx){
         --sx;
       }else if(*sx == '$'){
         x = 0;
-        state = STATE_WANT_HASH;
+        state = STATE_WANT_DATA;
       }else if(*sx == '-'){
         x = 0;
         y += 6;