Fix textual palettes not accepting to be filled

A weird case of off-by-one error

src/gfx/pal_spec.cpp

@@ -371,13 +371,13 @@ static void parseGPLFile(std::filebuf &file) {
 			return;
 		}
 
-		++nbColors;
 		if (nbColors < maxNbColors) {
-			if (nbColors % options.nbColorsPerPal == 1) {
+			if (nbColors % options.nbColorsPerPal == 0) {
 				options.palSpec.emplace_back();
 			}
 			options.palSpec.back()[nbColors % options.nbColorsPerPal] = *color;
 		}
+		++nbColors;
 	}
 
 	if (nbColors > maxNbColors) {
@@ -419,13 +419,13 @@ static void parseHEXFile(std::filebuf &file) {
 		Rgba color =
 		    Rgba(toHex(line[0], line[1]), toHex(line[2], line[3]), toHex(line[4], line[5]), 0xFF);
 
-		++nbColors;
 		if (nbColors < maxNbColors) {
-			if (nbColors % options.nbColorsPerPal == 1) {
+			if (nbColors % options.nbColorsPerPal == 0) {
 				options.palSpec.emplace_back();
 			}
 			options.palSpec.back()[nbColors % options.nbColorsPerPal] = color;
 		}
+		++nbColors;
 	}
 
 	if (nbColors > maxNbColors) {

test/gfx/full_hex.flags

@@ -0,0 +1 @@
+-c hex:full_hex.hex

test/gfx/full_hex.hex

@@ -0,0 +1,39 @@
+e77300
+008cce
+634218
+000000
+
+efd600
+5ad639
+008cce
+000000
+
+efd600
+ef9c8c
+5ab5ef
+008cce
+
+efd600
+5ad639
+39217b
+000000
+
+efd600
+00ef63
+5ab5ef
+316331
+
+efd600
+adadc6
+ef9c8c
+5ab5ef
+
+e77300
+634218
+39217b
+000000
+
+5ad639
+316331
+39217b
+000000