Upgrade bundled nanosvg library to latest upstream commit

commit 706eb0618249507c1700cef4a518f73e546b1c38 (upstream/master)
Author: Mikko Mononen <memononen@gmail.com>
Date:   Wed Nov 22 22:47:18 2023 +0200

    Merge pull request #249 from wcout/issue_240

    Fix for #240: Bug: "else" missing

+ FLTK specific extensions, see documentation/src/bundled-libs.dox

documentation/src/bundled-libs.dox

@@ -27,7 +27,7 @@ Current versions of bundled libraries (as of November 29, 2023):
   Library       Version/git commit Release date         FLTK Version
   --------------------------------------------------------------------------
   jpeg          jpeg-9e            2022-01-16           1.4.0
-  nanosvg       abcd277ea4 [1]     2022-12-22           1.4.0
+  nanosvg       7aeda550a8 [1]     2023-12-02           1.4.0
   png           libpng-1.6.40      2023-06-21           1.4.0
   zlib          zlib-1.3           2023-08-18           1.4.0
   libdecor      060fe761   [2]     2023-12-01           1.4.0

nanosvg/nanosvgrast.h

@@ -346,6 +346,7 @@ static float nsvg__normalize(float *x, float* y)
 }
 
 static float nsvg__absf(float x) { return x < 0 ? -x : x; }
+static float nsvg__roundf(float x) { return (x >= 0) ? floorf(x + 0.5) : ceilf(x - 0.5); }
 
 static void nsvg__flattenCubicBez(NSVGrasterizer* r,
 								  float x1, float y1, float x2, float y2,
@@ -888,10 +889,10 @@ static NSVGactiveEdge* nsvg__addActive(NSVGrasterizer* r, NSVGedge* e, float sta
 //	STBTT_assert(e->y0 <= start_point);
 	// round dx down to avoid going too far
 	if (dxdy < 0)
-		z->dx = (int)(-floorf(NSVG__FIX * -dxdy));
+		z->dx = (int)(-nsvg__roundf(NSVG__FIX * -dxdy));
 	else
-		z->dx = (int)floorf(NSVG__FIX * dxdy);
-	z->x = (int)floorf(NSVG__FIX * (e->x0 + dxdy * (startPoint - e->y0)));
+		z->dx = (int)nsvg__roundf(NSVG__FIX * dxdy);
+	z->x = (int)nsvg__roundf(NSVG__FIX * (e->x0 + dxdy * (startPoint - e->y0)));
 //	z->x -= off_x * FIX;
 	z->ey = e->y1;
 	z->next = 0;
@@ -1298,7 +1299,7 @@ static void nsvg__initPaint(NSVGcachedPaint* cache, NSVGpaint* paint, float opac
 	if (grad->nstops == 0) {
 		for (i = 0; i < 256; i++)
 			cache->colors[i] = 0;
-	} if (grad->nstops == 1) {
+	} else if (grad->nstops == 1) {
 		for (i = 0; i < 256; i++)
 			cache->colors[i] = nsvg__applyOpacity(grad->stops[i].color, opacity);
 	} else {