Removed unnecessary else and added guard clauses

As the title says, I've removed some unnecessary "else return" statements, and added some guard clauses so we don't have to go another level of indentation in the code.

olcPixelGameEngine.h

@@ -194,7 +194,7 @@
 
 	Author
 	~~~~~~
-	David Barr, aka javidx9, ©OneLoneCoder 2018, 2019, 2020, 2021
+	David Barr, aka javidx9, ©OneLoneCoder 2018, 2019, 2020, 2021
 */
 #pragma endregion
 
@@ -1306,14 +1306,10 @@ namespace olc
 		{
 			if (x >= 0 && x < width && y >= 0 && y < height)
 				return pColData[y * width + x];
-			else
 			return Pixel(0, 0, 0, 0);
 		}
-		else
-		{
 		return pColData[abs(y % height) * width + abs(x % width)];
 	}
-	}
 
 	bool Sprite::SetPixel(int32_t x, int32_t y, Pixel p)
 	{
@@ -1322,7 +1318,6 @@ namespace olc
 			pColData[y * width + x] = p;
 			return true;
 		}
-		else
 		return false;
 	}
 
@@ -1438,13 +1433,10 @@ namespace olc
 			pDecal = std::make_unique<olc::Decal>(pSprite.get(), filter, clamp);
 			return olc::rcode::OK;
 		}
-		else
-		{
 		pSprite.release();
 		pSprite = nullptr;
 		return olc::rcode::NO_FILE;
 	}
-	}
 
 	olc::Decal* Renderable::Decal() const
 	{ return pDecal.get(); }
@@ -1764,7 +1756,6 @@ namespace olc
 	{
 		if (pDrawTarget)
 			return pDrawTarget->width;
-		else
 		return 0;
 	}
 
@@ -1772,7 +1763,6 @@ namespace olc
 	{
 		if (pDrawTarget)
 			return pDrawTarget->height;
-		else
 		return 0;
 	}
 
@@ -1830,9 +1820,7 @@ namespace olc
 		if (!pDrawTarget) return false;
 
 		if (nPixelMode == Pixel::NORMAL)
-		{
 			return pDrawTarget->SetPixel(x, y, p);
-		}
 
 		if (nPixelMode == Pixel::MASK)
 		{
@@ -1852,9 +1840,7 @@ namespace olc
 		}
 
 		if (nPixelMode == Pixel::CUSTOM)
-		{
 			return pDrawTarget->SetPixel(x, y, funcPixelMode(x, y, p, pDrawTarget->GetPixel(x, y)));
-		}
 
 		return false;
 	}
@@ -1952,6 +1938,10 @@ namespace olc
 
 		if (radius > 0)
 		{
+			Draw(x, y, p);
+			return;
+		}
+
 		int x0 = 0;
 		int y0 = radius;
 		int d = 3 - 2 * radius;
@@ -1977,9 +1967,6 @@ namespace olc
 				d += 4 * (x0++ - y0--) + 10;
 		}
 	}
-		else
-			Draw(x, y, p);
-	}
 
 	void PixelGameEngine::FillCircle(const olc::vi2d& pos, int32_t radius, Pixel p)
 	{ FillCircle(pos.x, pos.y, radius, p); }
@@ -1991,6 +1978,10 @@ namespace olc
 
 		if (radius > 0)
 		{
+			Draw(x, y, p);
+			return;
+		}
+
 		int x0 = 0;
 		int y0 = radius;
 		int d = 3 - 2 * radius;
@@ -2019,9 +2010,6 @@ namespace olc
 			}
 		}
 	}
-		else
-			Draw(x, y, p);
-	}
 
 	void PixelGameEngine::DrawRect(const olc::vi2d& pos, const olc::vi2d& size, Pixel p)
 	{ DrawRect(pos.x, pos.y, size.x, size.y, p); }
@@ -2552,8 +2540,9 @@ namespace olc
 		di.uv = { { 0.0f, 0.0f}, {0.0f, 1.0f}, {1.0f, 1.0f}, {1.0f, 0.0f} };
 		olc::vf2d center;
 		float rd = ((pos[2].x - pos[0].x) * (pos[3].y - pos[1].y) - (pos[3].x - pos[1].x) * (pos[2].y - pos[0].y));
-		if (rd != 0)
-		{
+
+		if (rd == 0) return;
+
 		rd = 1.0f / rd;
 		float rn = ((pos[3].x - pos[1].x) * (pos[0].y - pos[1].y) - (pos[3].y - pos[1].y) * (pos[0].x - pos[1].x)) * rd;
 		float sn = ((pos[2].x - pos[0].x) * (pos[0].y - pos[1].y) - (pos[2].y - pos[0].y) * (pos[0].x - pos[1].x)) * rd;
@@ -2568,7 +2557,6 @@ namespace olc
 		di.mode = nDecalMode;
 		vLayers[nTargetLayer].vecDecalInstance.push_back(di);
 	}
-	}
 
 	void PixelGameEngine::DrawWarpedDecal(olc::Decal* decal, const std::array<olc::vf2d, 4>& pos, const olc::Pixel& tint)
 	{ DrawWarpedDecal(decal, pos.data(), tint); }