cg_particles: do not return previous particle pointer if maximum is hit

Fix random substitution of particles.

I noticed there was no error message for MAX_PARTICLE_SYSTEMS being hit.
I noticed there was an error message for MAX_TRAIL_SYSTEMS being hit.

So I wanted to add such error message to debug the random substitution
of particles

So I decided to copy-paste the MAX_TRAIL_SYSTEMS hit message and
implement it for MAX_PARTICLE_SYSTEMS the cargo cult way.

So I discovered the particle code was not only not printing anything
when MAX_PARTICLE_SYSTEMS was hit, but was also returning the particle
system anyway, the previous one before hitting MAX_PARTICLE_SYSTEMS.

Then I discovered a similar unexpected return of reused pointer
was also done when MAX_PARTICLES and MAX_PARTICLE_EJECTORS were hit.

- Do not return previous particle if MAX_PARTICLES is hit
- Do not return previous particle system if MAX_PARTICLE_SYSTEMS is hit
- Do not return previous particle ejector if MAX_PARTICLE_EJECTORS is hit

This is a port of a patch from Unvanquished: https://unvanquished.net

src/cgame/cg_particles.c

@@ -304,11 +304,14 @@ static particle_t *CG_SpawnNewParticle( baseParticle_t *bp, particleEjector_t *p
         }
       }
 
-      break;
+      return p;
     }
   }
 
-  return p;
+  if( cg_debugParticles.integer >= 1 )
+    CG_Printf( "MAX_PARTICLES\n" );
+
+  return NULL;
 }
 
 
@@ -426,11 +429,14 @@ static particleEjector_t *CG_SpawnNewParticleEjector( baseParticleEjector_t *bpe
       if( cg_debugParticles.integer >= 1 )
         CG_Printf( "PE %s created\n", ps->class->name );
 
-      break;
+      return pe;
     }
   }
 
-  return pe;
+  if( cg_debugParticles.integer >= 1 )
+    CG_Printf( "MAX_PARTICLE_EJECTORS\n" );
+
+  return NULL;
 }
 
 
@@ -473,11 +479,14 @@ particleSystem_t *CG_SpawnNewParticleSystem( qhandle_t psHandle )
       if( cg_debugParticles.integer >= 1 )
         CG_Printf( "PS %s created\n", bps->name );
 
-      break;
+      return ps;
     }
   }
 
-  return ps;
+  if( cg_debugParticles.integer >= 1 )
+    CG_Printf( "MAX_PARTICLE_SYSTEMS\n" );
+
+  return NULL;
 }
 
 /*