Add zero-range guard to map() to prevent NaN/Infinity when start1 equals stop1

Most appropriate sub-area of p5.js?

• Accessibility
• Color
• Core/Environment/Rendering
• Data
• DOM
• Events
• Image
• IO
• Math
• Typography
• Utilities
• p5.strands
• WebGL
• DevOps, Build process, Unit testing
• Internationalization (i18n)
• Friendly Errors
• Other (specify if possible)

p5.js version

Latest main branch (development version from the repository)

Web browser and version

All browsers — issue is in core math logic, not rendering

Operating system

macOS (development environment)

Steps to reproduce this

Steps:

1. Call map() with a collapsed input range (start1 === stop1)
2. Example: map(5, 10, 10, 0, 100)
3. The result becomes Infinity or NaN due to division by zero

Snippet:

// This produces Infinity or NaN:
let x = map(5, 10, 10, 0, 100);
console.log(x); // Infinity or NaN

Start by locating p5.js's map() entry point and reproduce map(5, 10, 10, 0, 100). Check the surrounding map tests or conventions to determine the intended result for a collapsed input range. Done means this case has defined behavior and no longer produces NaN or Infinity.